55 articles on Friday, September 21


arXiv:1809.07322v1 [pdf, other]
The MUSCLES Treasury Survey. V. FUV Flares on Active and Inactive M Dwarfs
Comments: Accepted to ApJ

M dwarf stars are known for their vigorous flaring. This flaring could impact the climate of orbiting planets, making it important to characterize M dwarf flares at the short wavelengths that drive atmospheric chemistry and escape. We conducted a far-ultraviolet flare survey of 6 M dwarfs from the recent MUSCLES (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems) observations, as well as 4 highly-active M dwarfs with archival data. When comparing absolute flare energies, we found the active-M-star flares to be about 10$\times$ more energetic than inactive-M-star flares. However, when flare energies were normalized by the star's quiescent flux, the active and inactive samples exhibited identical flare distributions, with a power-law index of -$0.76^{+0.09}_{-0.1}$ (cumulative distribution). The rate and distribution of flares are such that they could dominate the FUV energy budget of M dwarfs, assuming the same distribution holds to flares as energetic as those cataloged by Kepler and ground-based surveys. We used the observed events to create an idealized model flare with realistic spectral and temporal energy budgets to be used in photochemical simulations of exoplanet atmospheres. Applied to our own simulation of direct photolysis by photons alone (no particles), we find the most energetic observed flares have little effect on an Earth-like atmosphere, photolyzing $\sim$0.01% of the total O$_3$ column. The observations were too limited temporally (73 h cumulative exposure) to catch rare, highly energetic flares. Those that the power-law fit predicts occur monthly would photolyze $\sim$1% of the O$_3$ column and those it predicts occur yearly would photolyze the full O$_3$ column. Whether such energetic flares occur at the rate predicted is an open question.


arXiv:1809.07323v1 [pdf, other]
Blazar jets as the most efficient persistent engines
Comments: 12 pages, 4 figures, Invited talk at the meeting: A Decade of Agile: Results, Challenges and Prospects of Gamma-Ray Astrophysics. In memory of Giovanni Fabrizio "Nanni" Bignami. Accademia dei Lincei, December 2017

We have not identified for sure what is the mechanism launching, accelerating and collimating relativistic jets. The two most likely possibilities are the gravitational energy of the accreting matter or the rotational energy of a spinning black hole. Even the evaluation of the jet power is not trivial, since the radiation from the jet is enhanced by relativistic beaming, and there are fundamental uncertainties concerning the matter content of the jet (electron--proton or electron--positron plasma). However, in recent years, there have been crucial advances mainly driven by the richness of data in the $\gamma$-ray band. This is the band where blazars emit most of their electromagnetic power. Furthermore, there are now large sample of $\gamma$-ray loud blazars covered by optical spectroscopy. For the blazar sub-class of flat spectrum radio quasars (FSRQ) these data provide measurements of the main emission lines and of the underlying continuum. From these data, it is relatively easy to infer the bolometric luminosity of the accretion disk. The relativistic jet emission on one hand, and the disk luminosity on the other hand, allows us to compare the jet power and the accretion luminosity. Although the inferred jet power is subject to a few assumptions and is somewhat model--dependent, it is possible to derive a lower limit to the jet power that is assumption-free and model-independent. Since this lower limit is of the order of the accretion luminosity, we infer that the true jet power is larger.


arXiv:1809.07326v1 [pdf, other]
An accurate physical model for halo concentrations
Comments: 15 pages, 7 figures. Submitted to ApJ. Comments welcome. Code available at https://bitbucket.org/bdiemer/colossus

The relation between halo mass, M, and concentration, c, is a critical component in our understanding of the structure of dark matter halos. While numerous models for this relation have been proposed, almost none of them attempt to derive the evolution of the relation analytically. We build on previous efforts to model the c-M relation as a function of physical parameters such as the peak height, $\nu$, and the effective power spectrum slope, $n_{\rm eff}$, which capture the dependence of c on halo mass, redshift, and cosmology. We present three major improvements over previous models. First, we derive an analytical expression for the c-M relation which is valid under the assumption of pseudo-evolution, i.e., assuming that the density profiles of halos are static in physical coordinates while the definition of their boundary evolves. We find that this ansatz is highly successful in describing the evolution of the low-mass end of the c-M relation. Second, we employ a new physical variable, the effective exponent of linear growth, $\alpha_{\rm eff}$, to parameterize deviations from an Einstein-deSitter expansion history. Third, we combine an updated definition of $n_{\rm eff}$ with the additional dependence on $\alpha_{\rm eff}$ and propose a phenomenological extension of our analytical framework to include all halo masses. This semi-analytical model matches simulated concentrations in both scale-free models and LambdaCDM to 5% accuracy with very few exceptions and differs significantly from all previously proposed models. We present publicly available code to compute the predictions of our model in the python toolkit Colossus.


arXiv:1809.07328v1 [pdf, other]
What Sets the Slope of the Molecular Kennicutt-Schmidt Relation?
Comments: 13 pages, 11 figures + appendix. Submitted to ApJ. Comments are welcome

The surface densities of molecular gas, $\Sigma_{\rm H_2}$, and star formation rate (SFR), $\dot\Sigma_\star$, correlate almost linearly on kiloparsec scales in the observed star-forming (non-starburst) galaxies. We explore the origin of the linear slope of this correlation using a suite of isolated $L_\star$ galaxy simulations. We show that in simulations with efficient feedback, the slope of the $\dot\Sigma_\star$-$\Sigma_{\rm H_2}$ relation on kiloparsec scales is insensitive to the slope of the $\dot\rho_\star$-$\rho$ relation assumed at the resolution scale. We also find that the slope on kiloparsec scales depends on the criteria used to identify star-forming gas, with a linear slope arising in simulations that identify star-forming gas using a virial parameter threshold. This behavior can be understood using a simple theoretical model based on conservation of interstellar gas mass as the gas cycles between atomic, molecular, and star-forming states under the influence of feedback and dynamical processes. In particular, we show that the linear slope emerges when feedback efficiently regulates and stirs the evolution of dense, molecular gas. We show that the model also provides insights into the likely origin of the relation between the SFR and molecular gas in real galaxies on different scales.


arXiv:1809.07329v1 [pdf, other]
The ASAS-SN Catalog of Variable Stars II: Uniform Classification of 412,000 Known Variables
Comments: 37 pages, 42 figures, 11 tables. Submitted to MNRAS. The catalog of variable stars and the V-band light curves are available from the ASAS-SN Variable Stars Database at https://asas-sn.osu.edu/variables

The variable stars in the VSX catalog are derived from a multitude of inhomogeneous data sources and classification tools. This inhomogeneity complicates our understanding of variable star types, statistics, and properties, and it directly affects attempts to build training sets for current (and next) generation all-sky, time-domain surveys. We homogeneously analyze the ASAS-SN V-band light curves of ${\sim}412,000$ variables from the VSX catalog. The variables are classified using an updated random forest classifier with an $F_1$ score of 99.4% and refinement criteria for individual classifications. We have derived periods for ${\sim}44,000$ variables in the VSX catalog that lack a period, and have reclassified ${\sim} 17,000$ sources into new broad variability groups with high confidence. We have also reclassified ${\sim} 94,000$ known variables with miscellaneous/generic classifications. The light curves, classifications, and a range of properties of the variables are all available through the ASAS-SN variable stars database (https://asas-sn.osu.edu/variables). We also include the V-band light curves for a set of ${\sim}4,000$ rare variables and transient sources, including cataclysmic variables, symbiotic binaries and flare stars.


arXiv:1809.07330v1 [pdf, other]
A feasibility study on the photometric detection of quiescent black hole X-ray binaries
Comments: Accepted for publication in MNRAS, 11 pages, 5 figures, 3 Tables

We investigate the feasibility of detecting quiescent black hole X-ray binaries using optical photometric techniques. To test this we employ a combination of r-band and Halpha filters currently available at the Roque de los Muchachos Observatory. Photometric observations of four dynamical black holes (GRO J0422+320, A0620-00, XTE J1118+480 and XTE J1859+226) at SNR>~35-50, supplemented with near simultaneous spectroscopic data, demonstrate that it is possible to recover the FWHM of the Halpha emission line to better than 10% for targets with a wide range of line EWs and down to magnitude r~22. We further explore the potential of our photometric system to disentangle other populations of compact stars and Halpha emitters. In particular, we show that HAWKs, a survey designed to unveil quiescent black holes, will also provide a detailed census of other Galactic populations, most notably short period (eclipsing) cataclysmic variables, neutron star X-ray binaries and ultra-compact binaries.


arXiv:1809.07333v1 [pdf, other]
Consistency tests in cosmology using relative entropy
Comments: 31 pages, 9 figures, 4 tables, to be submitted to JCAP

With the high-precision data from current and upcoming experiments, it becomes increasingly important to perform consistency tests of the standard cosmological model. In this work, we focus on consistency measures between different data sets and methods that allow us to assess the goodness of fit of different models. We address both of these questions using the relative entropy or Kullback-Leibler (KL) divergence [Kullback et al., 1951]. First, we revisit the relative entropy as a consistency measure between data sets and further investigate some of its key properties, such as asymmetry and path dependence. We then introduce a novel model rejection framework, which is based on the relative entropy and the posterior predictive distribution. We validate the method on several toy models and apply it to Type Ia supernovae data from the JLA and CMB constraints from Planck 2015, testing the consistency of the data with six different cosmological models.


arXiv:1809.07335v1 [pdf, other]
Longterm properties of accretion discs in X-ray Binaries - III. A search for spin-superorbital correlation in SMC X-1
Comments: 16 pages, 12 figures

Thanks to long-term X-ray monitoring, a number of interacting binaries are now known to show X-ray periodicities on timescales of tens to hundreds of binary orbits. In some systems, precession of a warped accretion disc is the leading model to explain the superorbital modulation. The High Mass X-ray Binary SMC X-1 showed two excursions in superorbital period (from ~60d to ~45d) during the 1996-2011 interval, suggesting that some characteristic of the accretion disc is varying on a timescale of years. Because its behaviour as an X-ray pulsar has also been intensively monitored, SMC X-1 offers the rare chance to track changes in both the accretion disk and pulsar behaviours over the same interval. We have used archival X-ray observations of SMC X-1 to investigate whether the evolution of its superorbital variation and pulse period are correlated. We use the 16-year dataset afforded by the RXTE~All-Sky Monitor to trace the behaviour of the warped accretion disc in this system, and use published pulse-period histories to trace the behaviour of the pulsar. While we cannot claim a strong detection of correlation, the first superorbital period excursion near MJD 50,800 does coincide with structure in SMC X-1's pulse period history. Our preferred interpretation is that the superorbital period excursion coincides with a change in the long-term spin-up rate of the SMC X-1 pulsar. In this scenario, the pulsar and the accretion disc are both responding to a change in the accretion flow, which the disc itself may regulate.


arXiv:1809.07336v1 [pdf, other]
JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies: I. Survey overview and first results
Comments: MNRAS in press, 25 pages

JINGLE is a new JCMT legacy survey designed to systematically study the cold interstellar medium of galaxies in the local Universe. As part of the survey we perform 850um continuum measurements with SCUBA-2 for a representative sample of 193 Herschel-selected galaxies with M*>10^9Msun, as well as integrated CO(2-1) line fluxes with RxA3m for a subset of 90 of these galaxies. The sample is selected from fields covered by the Herschel-ATLAS survey that are also targeted by the MaNGA optical integral-field spectroscopic survey. The new JCMT observations combined with the multi-wavelength ancillary data will allow for the robust characterization of the properties of dust in the nearby Universe, and the benchmarking of scaling relations between dust, gas, and global galaxy properties. In this paper we give an overview of the survey objectives and details about the sample selection and JCMT observations, present a consistent 30 band UV-to-FIR photometric catalog with derived properties, and introduce the JINGLE Main Data Release (MDR). Science highlights include the non-linearity of the relation between 850um luminosity and CO line luminosity, and the serendipitous discovery of candidate z>6 galaxies.


arXiv:1809.07337v1 [pdf, other]
SDSS J0909$+$4449: A Large-separation Strongly Lensed Quasar at $z \sim 2.8$ with Three Images
Comments: 5 pages, 3 figures, accepted for publication in the MNRAS Letter

We report the discovery of SDSS J0909$+$4449, an exceptional system consisting of a quasar at $z=2.788$ strongly lensed by a group of galaxies at $z \sim 0.9$ into three images separated by up to 14\arcsec\, based on archival data collected by the Sloan Digital Sky Survey, extended Baryon Oscillation Spectroscopic Survey, Beijing--Arizona Sky Survey, the Mayall z-band Legacy Survey, and the Gemini Telescope. We discuss two hypotheses on the nature of SDSS J0909$+$4449, i.e. a rare triply-imaged quasar in the naked cusp configuration and a typical quadruply-imaged quasar with the fourth image undetected in the current data. We find that simple lens models can provide excellent fits to the observed image positions and the non-detection under either hypothesis. Deeper imaging data, spectroscopic observations, and follow-up light curve measurements will be helpful in determining which hypothesis is correct and provide better constraints on the lens mass distribution. Nevertheless, given its unusually large image separations, SDSS J0909$+$4449 will be a unique probe for the mass structure and the underlying cooling and stellar feedback processes on group or cluster scales.


arXiv:1809.07339v1 [pdf, other]
The Keplerian three-body encounter I. Insights on the origin of the S-stars and the G-objects in the Galactic center
Comments: 8 pages, 7 figures, submitted to ApJ

Recent spectroscopic analysis has set an upper limit to the age of the S-stars, the ~30 B-type stars on highly eccentric orbits around the supermassive black hole (SMBH) in the Galactic center. The inferred age (<15 Myr) is in tension with the binary break-up scenario for their origin. However, it is curiously compatible with the age of the disk of O-type stars that lies at a farther distance from the SMBH. Here we investigate a new formation scenario, assuming that the both S-stars and the O-type stars were born in the same disk around SgrA*. We simulate encounters between binaries of the stellar disk and stellar black holes from a dark cusp around SgrA*. We find that B-type binaries can get easily disrupted by the encounters and their binary components are kicked into highly eccentric orbits around the SMBH. In contrast, O-type binaries are less frequently disrupted and their members remain on low eccentric orbits. This mechanism can reproduce 11 S-stars just by assuming that the binaries initially lie within the stellar disk as observed nowadays. To reproduce all the S-stars, the original disk must have been extended down to 0.006 pc. However in this case many B- and O-type stars remain on low eccentricity orbits below 0.03 pc, in contrast with the observations. Therefore, some other mechanism is necessary to disperse the disk below 0.03 pc. This scenario can also explain the high eccentricity of the G-objects, if they have a stellar origin.


arXiv:1809.07340v1 [pdf, other]
A novel 3D technique to study the kinematics of lensed galaxies
Comments: Accepted for publication in MNRAS

We present a 3D Bayesian method to model the kinematics of strongly lensed galaxies from spatially-resolved emission-line observations. This technique enables us to simultaneously recover the lens-mass distribution and the source kinematics directly from the 3D data cube. We have tested this new method with simulated OSIRIS observations for nine star-forming lensed galaxies with different kinematic properties. The simulated rotation curves span a range of shapes which are prototypes of different morphological galaxy types, from dwarf to massive spiral galaxies. We have found that the median relative accuracy on the inferred lens and kinematic parameters are at the level of 1 and 2 per cent, respectively. We have also tested the robustness of the technique against different inclination angles, signal-to-noise ratios, the presence of warps or non-circular motions and we have found that the accuracy stays within a few per cent in most cases. This technique represents a significant step forward with respect to the methods used until now, as the lens parameters and the kinematics of the source are derived from the same 3D data. This enables us to study the possible degeneracies between the two and estimate the uncertainties on all model parameters consistently.


arXiv:1809.07341v1 [pdf, other]
Survey of Gravitationally-lensed Objects in HSC Imaging (SuGOHI). II. Environments and Line-of-Sight Structure of Strong Gravitational Lens Galaxies to z ~ 0.8
Comments: Accepted for publication in the Astrophysical Journal; 22 pages, 10 figures, 9 tables

We investigate the local and line-of-sight overdensities of strong gravitational lens galaxies using wide-area multiband imaging from the Hyper Suprime-Cam Subaru Strategic Program. We present 41 new definite or probable lens candidates discovered in Data Release 2 of the survey. Using a combined sample of 87 galaxy-scale lenses out to a lens redshift of $z_{\mathrm{L}} \sim 0.8$, we compare galaxy number counts in lines of sight toward known and newly-discovered lenses in the survey to those of a control sample consisting of random lines of sight. We also compare the local overdensity of lens galaxies to a sample of "twin" galaxies that have a similar redshift and velocity dispersion to test whether lenses lie in different environments from similar non-lens galaxies. We find that lens fields contain higher number counts of galaxies compared to the control fields, but this effect arises from the local environment of the lens. Once galaxies in the lens plane are removed, the lens lines of sight are consistent with the control sample. The local environments of the lenses are overdense compared to the control sample, and are slightly overdense compared to those of the twin sample, although the significance is marginal. There is no significant evidence of the evolution of the local overdensity of lens environments with redshift.


arXiv:1809.07342v1 [pdf, other]
Far-Ultraviolet Activity Levels of F, G, K, and M dwarf Exoplanet Host Stars
Comments: ApJS, accepted. 33 pages in emulateapj, 13 figures, 10 tables

We present a survey of far-ultraviolet (FUV; 1150 - 1450 Ang) emission line spectra from 71 planet-hosting and 33 non-planet-hosting F, G, K, and M dwarfs with the goals of characterizing their range of FUV activity levels, calibrating the FUV activity level to the 90 - 360 Ang extreme-ultraviolet (EUV) stellar flux, and investigating the potential for FUV emission lines to probe star-planet interactions (SPIs). We build this emission line sample from a combination of new and archival observations with the Hubble Space Telescope-COS and -STIS instruments, targeting the chromospheric and transition region emission lines of Si III, N V, C II, and Si IV. We find that the exoplanet host stars, on average, display factors of 5 - 10 lower UV activity levels compared with the non-planet hosting sample; this is explained by a combination of observational and astrophysical biases in the selection of stars for radial-velocity planet searches. We demonstrate that UV activity-rotation relation in the full F - M star sample is characterized by a power-law decline (with index $\alpha$ ~ -1.1), starting at rotation periods >~3.5 days. Using N V or Si IV spectra and a knowledge of the star's bolometric flux, we present a new analytic relationship to estimate the intrinsic stellar EUV irradiance in the 90 - 360 Ang band with an accuracy of roughly a factor of ~2. Finally, we study the correlation between SPI strength and UV activity in the context of a principal component analysis that controls for the sample biases. We find that SPIs are not a statistically significant contributor to the observed UV activity levels.


arXiv:1809.07343v1 [pdf, other]
Superluminous Supernovae in LSST: Rates, Detection Metrics, and Light Curve Modeling
Comments: 13 pages, 11 figures, submitted to ApJ

We explore and demonstrate the capabilities of LSST to study Type I superluminous supernovae (SLSNe). We first fit the light curves of 58 known SLSNe at z~0.1-1.6, using an analytical magnetar spin-down model implemented in MOSFiT. We then use the posterior distributions of the magnetar and ejecta parameters to generate thousands of synthetic SLSN light curves, and we inject those into the OpSim to generate realistic ugrizy light curves. We define simple, measurable metrics to quantify the detectability and utility of the light curve, and to measure the efficiency of LSST in returning SLSN light curves satisfying these metrics. We combine the metric efficiencies with the volumetric rate of SLSNe to estimate the overall discovery rate of LSST, and we find that ~10^4 SLSNe per year with >10 data points will be discovered in the WFD survey at z<3.0, while only ~15 SLSNe per year will be discovered in each DDF at z<4.0. To evaluate the information content in the LSST data, we refit representative output light curves with the same model that was used to generate them. We correlate our ability to recover magnetar and ejecta parameters with the simple light curve metrics to evaluate the most important metrics. We find that we can recover physical parameters to within 30% of their true values from ~18% of WFD light curves. Light curves with measurements of both the rise and decline in gri-bands, and those with at least fifty observations in all bands combined, are most information rich, with ~30% of these light curves having recoverable physical parameters to ~30% accuracy. WFD survey strategies which increase cadence in these bands and minimize seasonal gaps will maximize the number of scientifically useful SLSN light curves. Finally, although the DDFs will provide more densely sampled light curves, we expect only ~50 SLSNe with recoverable parameters in each field in the decade-long survey.


arXiv:1809.07346v1 [pdf, other]
Coronal temperatures of the AGN ESO 103-035 and IGR 2124.7+5058 from NuSTAR observations
Comments: 9 pages, 7 figures, MNRAS accepted

We present measurements of the coronae of two AGN from hard X-ray observations made with NuSTAR: ESO 103-035, a moderately to highly obscured source with significant reflection; and IGR 2124.7+5058, a radio-loud source with a very hard spectrum. Using an exponentially cut-off powerlaw model for the coronal emission spectrum gives a high-energy cut-off of $100_{-30}^{+90}$ keV for ESO 103-035 and $80_{-9}^{+11}$ keV for IGR 2124.7+5058, within the typical range for AGN. Fitting with physical Comptonisation models shows that these correspond to a temperature of $22_{-6}^{+19}$ and $20_{-2}^{+3}$ keV respectively. These values are consistent with pair production limiting the coronal temperature.


arXiv:1809.07351v1 [pdf, other]
The Origins Space Telescope
Comments: Published in Nature Astronomy. This 7-page PDF is the submitted version - here is a free link to the published article: https://rdcu.be/3Rtt

The Origins Space Telescope, one of four large Mission Concept studies sponsored by NASA for review in the 2020 US Astrophysics Decadal Survey, will open unprecedented discovery space in the infrared, unveiling our cosmic origins. We briefly describe in this article the key science themes and architecture for OST. With a sensitivity gain of up to a factor of 1,000 over any previous or planned mission, OST will open unprecedented discovery space, allow us to peer through an infrared window teeming with possibility. OST will fundamentally change our understanding of our cosmic origins - from the growth of galaxies and black holes, to uncovering the trail of water, to life signs in nearby Earth-size planets, and discoveries never imagined. Built to be highly adaptable, while addressing key science across many areas of astrophysics, OST will usher in a new era of infrared astronomy.


arXiv:1809.07352v1 [pdf, other]
Milky Way metallicity gradient from Gaia DR2 F/1O double-mode Cepheids
Comments: 10 pages, 8 figures, accepted in A&A

The ratio of the first overtone (1O) / fundamental (F) periods of mixed-mode Cepheids that pulsate simultaneously in these two modes (F/1O) is metallicity-dependent. It can therefore be used to characterize the systems that host such variable stars. We want to take advantage of the F/1O double-mode Cepheids listed in the Gaia DR2 catalogue to derive the metallicity gradient in the Milky Way disk. The metallicity is derived from the ratio of the first overtone and fundamental periods provided by Gaia DR2 while the Gaia DR2 parallaxes are used to determine the Galactocentric distances of the stars. From a visual inspection of the light curves, it turns out that a large fraction (77%) of the Galactic F/1O double-mode Cepheids in Gaia DR2 are spurious detections. Gaia DR2 provides 3 new bona fide F/1O Cepheids. Combining them with the currently known F/1O Cepheids and using the Gaia DR2 parallaxes for the entire sample, we can derive the metallicity gradient in the Milky Way disk. We find a slope of -0.045$\pm$0.007 dex/kpc using a bootstrap method, and of -0.040$\pm$0.002 dex/kpc using a total least squares method. These results are in good agreement with previous determinations of the [Fe/H] gradient in the disk based on canonical Cepheids. The period ratio of F/1O Cepheids allows for a reliable determination of the metallicity gradient in the Milky Way, and in turn, in other systems that would be difficult to reach via classical spectroscopic methods.


arXiv:1809.07355v1 [pdf, other]
Correcting for Fibre Assignment Incompleteness in the DESI Bright Galaxy Survey
Comments: 18 pages, 17 figures, 4 tables, submitted to MNRAS

The Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) will be a survey of bright, low redshift galaxies, which is planned to cover an area of ~14,000 sq deg in 3 passes. Each pass will cover the survey area with ~2000 pointings, each of area ~8 sq deg. The BGS is currently proposed to consist of a bright high priority sample to an r-band magnitude limit r ~ 19.5, with a fainter low priority sample to r ~ 20. The geometry of the DESI fibre positioners in the focal plane of the telescope affects the completeness of the survey, and has a non-trivial impact on clustering measurements. Using a BGS mock catalogue, we show that completeness due to fibre assignment primarily depends on the surface density of galaxies. Completeness is high (>95%) in low density regions, but very low (<10%) in the centre of massive clusters. We apply the inverse pair weighting correction of Bianchi & Percival (2017) to clustering measurements from a BGS mock which has been through the fibre assignment algorithm. This method is only unbiased if it is possible to observe every galaxy pair. To facilitate this, we randomly promote a small fraction of the fainter sample to be high priority, and dither the set of tile positions by a small angle. We show that inverse pair weighting combined with angular upweighting provides an unbiased correction to galaxy clustering measurements for the complete 3 pass survey, and also after 1 pass, which is highly incomplete.


arXiv:1809.07373v1 [pdf, other]
Feedhorn development and scalability for Simons Observatory and beyond
Comments: No comment found

The Simons Observatory (SO) will measure the cosmic microwave background (CMB) in both temperature and polarization over a wide range of angular scales and frequencies from 27-270 GHz with unprecedented sensitivity. One technology for coupling light onto the $\sim$50 detector wafers that SO will field is spline-profiled feedhorns, which offer tunability between coupling efficiency and control of beam polarization leakage effects. We will present efforts to scale up feedhorn production for SO and their viability for future CMB experiments, including direct-machining metal feedhorn arrays and laser machining stacked Si arrays.


arXiv:1809.07374v1 [pdf, other]
Why do protoplanetary disks appear not massive enough to form the known exoplanet population?
Comments: Accepted to A&A Letter

When and how planets form in protoplanetary disks is still a topic of discussion. Exoplanet detection surveys and protoplanetary disk surveys are now providing results that allow us to have new insights. We collect the masses of confirmed exoplanets and compare their dependence with stellar mass with the same dependence for protoplanetary disk masses measured in ~1-3 Myr old star-forming regions. The latter are recalculated by us using the new estimates of their distances derived from Gaia DR2 parallaxes. We note that single and multiple exoplanetary systems form two different populations, probably pointing to a different formation mechanism for massive giant planets around very low mass stars. While expecting that the mass in exoplanetary systems is much lower than the measured disk masses, we instead find that exoplanetary systems masses are comparable or higher than the most massive disks. This same result is found also by converting the measured planet masses into heavy-element content (core masses for the giant planets and full masses for the super-Earth systems) and by comparing this value with the disk dust masses. Unless disk dust masses are heavily underestimated, this is a big conundrum. An extremely efficient recycling of dust particles in the disk cannot solve this conundrum. This implies that either the cores of planets have formed very rapidly (<0.1-1 Myr) and large amount of gas is expelled on the same timescales from the disk, or that disks are continuously replenished of fresh planet-forming material from the environment. These hypotheses can be tested by measuring disk masses in even younger targets and by better understanding if and how the disks are replenished by their surroundings.


arXiv:1809.07391v1 [pdf, other]
Observational diagnostics of elongated planet-induced vortices with realistic planet formation timescales
Comments: Submitted to MNRAS. Addressed first round of referee comments. 13 pages, 8 figures. Movies available at: https://lavinia.as.arizona.edu/~mhammer/vortex_signatures.html

Gap-opening planets can generate dust-trapping vortices that may explain some of the latest discoveries of high-contrast crescent-shaped dust asymmetries in transition discs. While planet-induced vortices were previously thought to have concentrated shapes, recent computational work has shown that these features naturally become much more elongated in the gas when simulations account for the relatively long timescale over which planets accrete their mass. In this work, we conduct two-fluid hydrodynamical simulations of vortices induced by slowly-growing Jupiter-mass planets in discs with very low viscosity ($\alpha = 3 \times 10^{-5}$). We simulate the dust dynamics for {\cbf four particle sizes spanning 0.3 mm to 1 cm in order to produce synthetic ALMA images. In our simulations, we find that an elongated vortex still traps dust, but not directly at its center. With a flatter pressure bump and disruptions from the planet's overlapping spiral density waves, the dust instead circulates around the vortex. This motion (1) typically carries the peak off-center, (2) spreads the dust out over a wider azimuthal extent $\geq 180^{\circ}$, (3) skews the azimuthal profile towards the front of the vortex, and (4) can also create double peaks in newly-formed vortices. The most defining signature, a peak offset of more than $30^{\circ}$, is detectable $>30\%$ of the time in observations with a beam diameter of at most the planet's separation from its star.


arXiv:1809.07393v1 [pdf, other]
The Draconid meteoroid stream 2018: prospects for satellite impact detection
Comments: Accepted for publication by APJ Letter the 19/09/2018

Predictions of the 2018 Draconid activity at the Earth and the Sun-Earth L1 and L2 Lagrange points are presented. Numerical simulations of the meteoroids' ejection and evolution from comet 21P/Giacobini-Zinner are performed with a careful implementation of the results analysis and weighting. Model meteoroid fluxes at Earth are derived using as calibration the main peak date, intensity, and shower profiles of previous Draconid outbursts. Good agreement between the model and measurements is found for the 1933, 1946, 1998 and 2011 showers for a meteoroid size distribution index at ejection of about 2.6. A less accurate estimate of the peak time for the 1985, 2005 and 2012 predominantly radio-observed outbursts was found by considering the contribution of individual ejection epochs, while the model peak flux estimate was found to agree with observations to within a factor 3. Despite the promising geometrical configuration in 2018, our simulations predict low Draconid activity is expected on Earth, with a maximum of less than a few tens of meteors per hour around midnight the 9th of October, confirming previous models. At the L1 and L2 Lagrange points, however, the flux estimates suggest a 'meteoroid storm'. The Gaia spacecraft at the L2 region might be able to detect small (~ {\mu}g) Draconid meteoroid impacts centered in a two-hour window around 18h30 UT on the 8th of October, 2018.


arXiv:1809.07403v1 [pdf, other]
TESS in the Solar System
Comments: Accepted for publication in PASP

The Transiting Exoplanet Survey Satellite (TESS), launched successfully on 18th of April, 2018, will observe nearly the full sky and will provide time-series imaging data in ~27-day-long campaigns. TESS is equipped with 4 cameras; each has a field-of-view of 24x24 degrees. During the first two years of the primary mission, one of these cameras, Camera #1, is going to observe fields centered at an ecliptic latitude of 18 degrees. While the ecliptic plane itself is not covered during the primary mission, the characteristic scale height of the main asteroid belt and Kuiper belt implies that a significant amount of small solar system bodies will cross the field-of-view of this camera. Based on the comparison of the expected amount of information of TESS and Kepler/K2, we can compute the cumulative etendues of the two optical setups. This comparison results in roughly comparable optical etendues, however the net etendue is significantly larger in the case of TESS since all of the imaging data provided by the 30-minute cadence frames are downlinked rather than the pre-selected stamps of Kepler/K2. In addition, many principles of the data acquisition and optical setup are clearly different, including the level of confusing background sources, full-frame integration and cadence, the field-of-view centroid with respect to the apparent position of the Sun, as well as the differences in the duration of the campaigns. As one would expect, TESS will yield time-series photometry and hence rotational properties for only brighter objects, but in terms of spatial and phase space coverage, this sample will be more homogeneous and more complete. Here we review the main analogues and differences between the Kepler/K2 mission and the TESS mission, focusing on scientific implications and possible yields related to our Solar System.


arXiv:1809.07431v1 [pdf, other]
Dwarf Galaxies as Cosmological Probes
Comments: Invited review at IAU Symposium 344, Dwarf Galaxies: From the Deep Universe to the Present

The Lambda Cold Dark Matter (LCDM) paradigm makes specific predictions for the abundance, structure, substructure and clustering of dark matter halos, the sites of galaxy formation. These predictions can be directly tested, in the low-mass halo regime, by dark matter-dominated dwarf galaxies. A number of potential challenges to LCDM have been identified when confronting the expected properties of dwarfs with observation. I review our understanding of a few of these issues, including the 'missing satellites' and the 'too-big-to-fail' problems, and argue that neither poses an insurmountable challenge to LCDM. Solving these problems requires that most dwarf galaxies inhabit halos of similar mass, and that there is a relatively sharp minimum halo mass threshold to form luminous galaxies. These predictions are eminently falsifiable. In particular, LCDM predicts a large number of 'dark' low-mass halos, some of which sould have retained enough primordial gas to be detectable in deep 21 cm or H$_\alpha$ surveys. Detecting this predicted population of 'mini-halos' would be a major discovery and a resounding success for LCDM on small scales.


arXiv:1809.07446v1 [pdf, other]
The Broad Absorption Line Tidal Disruption Event iPTF15af: Optical and Ultraviolet Evolution
Comments: 19 pages, 10 figures, submitted to ApJ

We present multiwavelength observations of the tidal disruption event (TDE) iPTF15af, discovered by the intermediate Palomar Transient Factory (iPTF) survey at redshift $z=0.07897$. The optical and ultraviolet (UV) light curves of the transient show a slow decay over five months, in agreement with previous optically discovered TDEs. It also has a comparable black-body peak luminosity of $L_{\rm{peak}} \approx 1.2 \times 10^{44}$ erg s$^{-1}$. The inferred temperature from the optical and UV data shows a constant value of (3$-$5) $\times 10^4$ K. The transient is not detected in X-rays up to $L_X < 3 \times 10^{42}$erg s$^{-1}$ within the first five months after discovery. The optical spectra exhibit two distinct broad emission lines in the He II region, and at later times also H$\alpha$ emission. Additionally, emission from [N III] and [O III] is detected, likely produced by the Bowen fluorescence effect. UV spectra reveal broad emission and absorption lines associated with high-ionization states of N V, C IV, Si IV, and possibly P V. These features, analogous to those of broad absorption line quasars (BAL QSOs), require an absorber with column densities $N_{\rm{H}} > 10^{23}$ cm$^{-2}$. This optically thick gas would also explain the nondetection in soft X-rays. The profile of the absorption lines with the highest column density material at the largest velocity is opposite that of BAL QSOs. We suggest that radiation pressure generated by the TDE flare at early times could have provided the initial acceleration mechanism for this gas. Spectral line monitoring of future TDEs could test this proposal.


arXiv:1809.07451v1 [pdf, other]
Blue Large-Amplitude Pulsators (BLAPs): possible origin, evolutionary status, and nature of their pulsations
Comments: 7 pages and 9 figures. Submitted as Proceedings for the 21st European White Dwarf Workshop held July 23-27, 2018, Austin, Texas

The Blue Large-Amplitude Pulsators (BLAPs) constitute a new class of pulsating stars. They are hot stars with effective temperatures of $T_{\rm eff}\sim 30\,000$ K and surface gravities of $\log g \sim 4.9$, that pulsate with periods in the range $\sim 20-40$ min. In Romero et al. (2018), we proposed that BLAPs are hot low-mass He-core pre-white dwarf (WD) stars that pulsate either in high-order non-radial $g$(gravity) modes or low-order radial modes, including the fundamental radial mode. The theoretical modes with periods in the observed range are unstable due to the $\kappa$ mechanism associated with the $Z$ bump in the opacity at $\log T \sim 5.25$. In this work, we extend the study of Romero et al. (2018) by assessing the rate of period changes of nonradial $g$ modes and radial modes and comparing them with the values measured for BLAPs, in an attempt to validate the proposed evolutionary scenario, and to discern whether the observed modes are high-order $g$ modes or radial modes.


arXiv:1809.07476v1 [pdf, other]
Direct Measurement of Quasar Outflow Wind Acceleration
Comments: 25 pages, including 6 figures; submitted to the Astrophysical Journal

We search for velocity changes (i.e., acceleration/deceleration) of narrow absorption lines (NALs) that are intrinsic to the quasars, using spectra of 6 bright quasars that have been observed more than once with 8-10m class telescopes. While variations in line strength and profile are frequently reported (especially in broader absorption lines), definitive evidence for velocity shifts has not been found with only a few exceptions. Direct velocity shift measurements are valuable constraints on the acceleration mechanisms. In this study, we determine velocity shifts by comparing the absorption profiles of NALs at two epochs separated by more than 10 years in the observed frame, using the cross-correlation function method and we estimate the uncertainties using Monte Carlo simulations. We do not detect any significant shifts but we obtain 3$\sigma$ upper limits on the acceleration of intrinsic NALs (compared to intervening NALs in same quasars) of $\sim$0.7 km s$^{-1}$ yr$^{-1}$ ($\sim$0.002 cm s$^{-2}$). We discuss possible scenarios for non-detection of NAL acceleration/deceleration and examine resulting constraints on the physical conditions in accretion disk wind.


arXiv:1809.07486v1 [pdf, other]
A geometrical 1% distance to the short-period binary Cepheid V1334 Cygni
Comments: Accepted for publication in ApJ

Cepheid stars play a considerable role as extragalactic distances indicators, thanks to the simple empirical relation between their pulsation period and their luminosity. They overlap with that of secondary distance indicators, such as Type Ia supernovae, whose distance scale is tied to Cepheid luminosities. However, the Period-Luminosity (P-L) relation still lacks a calibration to better than 5%. Using an original combination of interferometric astrometry with optical and ultraviolet spectroscopy, we measured the geometrical distance d = 720.35+/-7.84 pc of the 3.33 d period Cepheid V1334 Cyg with an unprecedented accuracy of +/-1 %, providing the most accurate distance for a Cepheid. Placing this star in the P-L diagram provides an independent test of existing period-luminosity relations. We show that the secondary star has a significant impact on the integrated magnitude, particularly at visible wavelengths. Binarity in future high precision calibrations of the P-L relations is not negligible, at least in the short-period regime. Subtracting the companion flux leaves V1334 Cyg in marginal agreement with existing photometric-based P-L relations, indicating either an overall calibration bias or a significant intrinsic dispersion at a few percent level. Our work also enabled us to determine the dynamical masses of both components, M1 = 4.288 +/- 0.133 Msun (Cepheid) and M2 = 4.040 +/- 0.048 Msun (companion), providing the most accurate masses for a Galactic binary Cepheid system.


arXiv:1809.07498v1 [pdf, other]
Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System
Comments: 44 pages, 19 figures, accepted for publication in the Astrophysical Journal

The TRAPPIST-1 planetary system provides an unprecedented opportunity to study terrestrial exoplanet evolution with the James Webb Space Telescope (JWST) and ground-based observatories. Since M dwarf planets likely experience extreme volatile loss, the TRAPPIST-1 planets may have highly-evolved, possibly uninhabitable atmospheres. We used a versatile, 1D terrestrial-planet climate model with line-by-line radiative transfer and mixing length convection (VPL Climate) coupled to a terrestrial photochemistry model to simulate environmental states for the TRAPPIST-1 planets. We present equilibrium climates with self-consistent atmospheric compositions, and observational discriminants of post-runaway, desiccated, 10-100 bar O2- and CO2-dominated atmospheres, including interior outgassing, as well as for water-rich compositions. Our simulations show a range of surface temperatures, most of which are not habitable, although an aqua-planet TRAPPIST-1 e could maintain a temperate surface given Earth-like geological outgassing and CO2. We find that a desiccated TRAPPIST-1 h may produce habitable surface temperatures beyond the maximum greenhouse distance. Potential observational discriminants for these atmospheres in transmission and emission spectra are influenced by photochemical processes and aerosol formation, and include collision-induced oxygen absorption (O2-O2), and O3, CO, SO2, H2O, and CH4 absorption features, with transit signals of up to 200 ppm. Our simulated transmission spectra are consistent with K2, HST, and Spitzer observations of the TRAPPIST-1 planets. For several terrestrial atmospheric compositions, we find that TRAPPIST-1 b is unlikely to produce aerosols. These results can inform JWST observation planning and data interpretation for the TRAPPIST-1 system and other M dwarf terrestrial planets.


arXiv:1809.07504v1 [pdf, other]
The polarization mode of the auroral radio emission from the early-type star HD142301
Comments: 5 pages, 4 figures; accepted to MNRAS Letters

We report the detection of the auroral radio emission from the early-type magnetic star HD142301. New VLA observations of HD142301 detected highly polarized amplified emission occurring at fixed stellar orientations. The coherent emission mechanism responsible for the stellar auroral radio emission amplifies the radiation within a narrow beam, making the star where this phenomenon occurs similar to a radio lighthouse. The elementary emission process responsible for the auroral radiation mainly amplifies one of the two magneto-ionic modes of the electromagnetic wave. This explains why the auroral pulses are highly circularly polarized. The auroral radio emission of HD142301 is characterized by a reversal of the sense of polarization as the star rotates. The effective magnetic field curve of HD142301 is also available making it possible to correlate the transition from the left to the right-hand circular polarization sense (and vice-versa) of the auroral pulses with the known orientation of the stellar magnetic field. The results presented in this letter have implications for the estimation of the dominant magneto-ionic mode amplified within the HD142301 magnetosphere.


arXiv:1809.07505v1 [pdf, other]
Rapidly-evolving episodic outflow in IRAS 18113-2503: clues to the ejection mechanism of the fastest water fountain
Comments: Preprint; accepted for publication in Monthly Notices of the Royal Astronomical Society Letters (September 17, 2018). Supplementary material is also included

Water fountains are evolved stars showing early stages of collimated mass loss during transition from the asymptotic giant branch, providing valuable insight into the formation of asymmetric planetary nebulae. We report the results of multi-epoch VLBI observations, which determine the spatial and three-dimensional kinematic structure of H$_2$O masers associated with the water fountain IRAS 18113-2503. The masers trace three pairs of high-velocity (~150-300 km s$^{-1}$) bipolar bow shocks on a scale of 0.18'' (~2000 au). The expansion velocities of the bow shocks exhibit an exponential decrease as a function of distance from the central star, which can be explained by an episodic, jet-driven outflow decelerating due to drag forces in a circumstellar envelope. Using our model, we estimate an initial ejection velocity ~840 km s$^{-1}$, a period for the ejections ~10 yr, with the youngest being ~12 yr old, and an average envelope density within the H$_2$O maser region $n_{\text{H}_2}$$\approx$$10^{6}$ cm$^{-3}$. We hypothesize that IRAS 18113-2503 hosts a binary central star with a separation of ~10 au, revealing novel clues about the launching mechanisms of high-velocity collimated outflows in water fountains.


arXiv:1809.07514v1 [pdf, other]
Exploring the Origins of Earth's Nitrogen: Astronomical Observations of Nitrogen-bearing Organics in Protostellar Environments
Comments: Accepted to ApJ; 21 pages, 4 figures

It is not known whether the original carriers of Earth's nitrogen were molecular ices or refractory dust. To investigate this question, we have used data and results of Herschel observations towards two protostellar sources: the high-mass hot core of Orion KL, and the low-mass protostar IRAS 16293-2422. Towards Orion KL, our analysis of the molecular inventory of Crockett et al. (2014) indicates that HCN is the organic molecule that contains by far the most nitrogen, carrying $74_{-9}^{+5}\%$ of nitrogen-in-organics. Following this evidence, we explore HCN towards IRAS 16293-2422, which we consider a solar analog. Towards IRAS 16293-2422, we have reduced and analyzed Herschel spectra of HCN, and fit these observations against "jump" abundance models of IRAS 16293-2422's protostellar envelope. We find an inner-envelope HCN abundance $X_{\textrm{in}} = 5.9\pm0.7 \times 10^{-8}$ and an outer-envelope HCN abundance $X_{\textrm{out}} = 1.3 \pm 0.1 \times 10^{-9}$. We also find the sublimation temperature of HCN to be $T_{\textrm{jump}} = 71 \pm 3$~K; this measured $T_{\textrm{jump}}$ enables us to predict an HCN binding energy $E_{\textrm{B}}/k = 3840 \pm 140$~K. Based on a comparison of the HCN/H2O ratio in these protostars to N/H2O ratios in comets, we find that HCN (and, by extension, other organics) in these protostars is incapable of providing the total bulk N/H2O in comets. We suggest that refractory dust, not molecular ices, was the bulk provider of nitrogen to comets. However, interstellar dust is not known to have 15N enrichment, while high 15N enrichment is seen in both nitrogen-bearing ices and in cometary nitrogen. This may indicate that these 15N-enriched ices were an important contributor to the nitrogen in planetesimals and likely to the Earth.


arXiv:1809.07528v1 [pdf, other]
Solenoidal improvements for the JF12 Galactic magnetic field model
Comments: 10 pages, 6 figures

The popular JF12 analytic model by Jansson & Farrar (2012) provides a quantitative description of the Galaxy's large-scale magnetic field that is widely used in various astrophysical applications. However, both the poloidal X-type component and the spiral disk component of JF12 exhibit regions in which the magnetic divergence constraint is severely violated. We first propose a cure for this problem, resulting in a truly solenoidal large-scale field. Second, the otherwise straight field lines of the X-type component exhibit kinks in the Galactic plane that, in addition to implying the presence of a singular current sheet, may pose difficulties for, e.g., numerical tracing of cosmic-ray particles. We propose and discuss two possible strategies to mitigate this problem. All corrections are kept as minimal as possible in order not to destroy the agreement to observational data that the unmodified JF12 field is based on. Furthermore, the performance of our improved version of the field model is quantitatively assessed by test simulations using the CRPropa Galactic cosmic-ray propagation code.


arXiv:1809.07551v1 [pdf, other]
Representative optical turbulence profiles for ESO Paranal by hierarchical clustering
Comments: Accepted MNRAS September 2018

Knowledge of the optical turbulence profile is important in adaptive optics (AO) systems, particularly tomographic AO systems such as those to be employed by the next generation of 40 m class extremely large telescopes (ELTs). Site characterisation and monitoring campaigns have produced large quantities of turbulence profiling data for sites around the world. However AO system design and performance characterisation is dependent on Monte-Carlo simulations that cannot make use of these large datasets due to long computation times. Here we address the question of how to reduce these large datasets into small sets of profiles that can feasibly be used in such Monte-Carlo simulations, whilst minimising the loss of information inherent in this effective compression of the data. We propose hierarchical clustering to partition the dataset according to the structure of the turbulence profiles and extract a single profile from each cluster. This method is applied to the Stereo-SCIDAR dataset from ESO Paranal containing over 10000 measurements of the turbulence profile from 83 nights. We present two methods of extracting turbulence profiles from the clusters, resulting in two sets of 18 profiles providing subtly different descriptions of the variability across the entire dataset. For generality we choose integrated parameters of the turbulence to measure the representativeness of our profiles and compare to others. Using these criterion we also show that such variability is difficult to capture with small sets of profiles associated with integrated turbulence parameters such as seeing.


arXiv:1809.07556v1 [pdf, other]
A NICER Discovery of a Low-Frequency QPO in the Soft-Intermediate State of MAXI J1535-571
Comments: Accepted for publication in ApJ Letters

We present the discovery of a low-frequency $\approx 5.7$ Hz quasi-periodic oscillation (QPO) feature in observations of the black hole X-ray binary MAXI J1535-571 in its soft-intermediate state, obtained in September-October 2017 by the Neutron Star Interior Composition Explorer (NICER). The feature is relatively broad (compared to other low-frequency QPOs; quality factor $Q\approx 2$) and weak (1.9% rms in 3-10 keV), and is accompanied by a weak harmonic and low-amplitude broadband noise. These characteristics identify it as a weak Type A/B QPO, similar to ones previously identified in the soft-intermediate state of the transient black hole X-ray binary XTE J1550-564. The lag-energy spectrum of the QPO shows increasing soft lags towards lower energies, approaching 50 ms at 1 keV (with respect to a 3-10 keV continuum). This large phase shift has similar amplitude but opposite sign to that seen in Rossi X-ray Timing Explorer data for a Type B QPO from the transient black hole X-ray binary GX 339-4. Previous phase-resolved spectroscopy analysis of the Type B QPO in GX 339-4 pointed towards a precessing jet-like corona illuminating the accretion disk as the origin of the QPO signal. We suggest that this QPO in MAXI J1535-571 may have the same origin, with the different lag sign depending on the scale height of the emitting region and the observer inclination angle.


arXiv:1809.07573v1 [pdf, other]
TESS's first planet: a super-Earth transiting the naked-eye star $π$ Mensae
Comments: Submitted to A&A. 10 pages, 5 figures, 5 tables

We report on the confirmation and mass determination of Pi Men c, the first transiting planet discovered by NASA's TESS space mission. Pi Men is a naked-eye (V=5.65 mag), quiet G0 V star that was previously known to host a sub-stellar companion (Pi Men b) on a long-period (Porb=2091 days), eccentric (e=0.64) orbit. Using TESS time-series photometry, combined with GAIA data, published UCLES@AAT Doppler measurements, and archival HARPS@ESO-3.6m radial velocities, we find that Pi Men c is an inner planet with an orbital period of Porb=6.25 days, a mass of Mp = 4.51 +/- 0.81 MEarth, and a radius of Rp = 1.828+/-0.053 REarth. Based on the planet's orbital period and size, Pi Men c is a super-Earth located at, or close to, the radius gap, while its mass and bulk density suggest it may have held on to a significant atmosphere. Because of the brightness of the host star, this system is highly suitable for a wide range of further studies to characterize the planetary atmosphere and dynamical properties. We also performed a seismic analysis of the TESS light curve and found a hint of an excess power at ~2600 micron-Hz with individual peaks spaced by ~120 micron-Hz. Though the signal-to-noise ratio is very low, this is consistent with the predicted frequency of oscillations for a star of this type, hinting at the asteroseismic potential of the TESS mission.


arXiv:1809.07578v1 [pdf, other]
Developing a self-consistent AGB wind model: I. Chemical, thermal, and dynamical coupling
Comments: Accepted for publication in MNRAS. 30 pages (incl. Appendix), 19 figures

The material lost through stellar winds of Asymptotic Giant Branch (AGB) stars is one of the main contributors to the chemical enrichment of galaxies. The general hypothesis of the mass loss mechanism of AGB winds is a combination of stellar pulsations and radiative pressure on dust grains, yet current models still suffer from limitations. Among others, they assume chemical equilibrium of the gas, which may not be justified due to rapid local dynamical changes in the wind. This is important as it is the chemical composition that regulates the thermal structure of the wind, the creation of dust grains in the wind, and ultimately the mass loss by the wind. Using a self-consistent hydrochemical model, we investigated how non-equilibrium chemistry affects the dynamics of the wind. This paper compares a hydrodynamical and a hydrochemical dust-free wind, with focus on the chemical heating and cooling processes. No sustainable wind arises in a purely hydrodynamical model with physically reasonable pulsations. Moreover, temperatures are too high for dust formation to happen, rendering radiative pressure on grains impossible. A hydrochemical wind is even harder to initiate due to efficient chemical cooling. However, temperatures are sufficiently low in dense regions for dust formation to take place. These regions occur close to the star, which is needed for radiation pressure on dust to sufficiently aid in creating a wind. Extending this model self-consistently with dust formation and evolution, and including radiation pressure, will help to understand the mass loss by AGB winds.


arXiv:1809.07581v1 [pdf, other]
Tomography of the red supergiant star μ Cep
Comments: 2 pages, 2 figures, accepted as Proceedings of IAU Symposium No. 343, 2018

A tomographic method, aiming at probing velocity fields at depth in stellar atmospheres, is applied to the red supergiant star {\mu} Cep and to snapshots of 3D radiative-hydrodynamics simulation in order to constrain atmospheric motions and relate them to photometric variability.


arXiv:1809.07588v1 [pdf, other]
AGN and Star Formation Feedback in Galaxy Outflows
Comments: 5 pages, 3 figures, paper to be published in the proceeding of IAU Symposium. 342: Perseus in Sicily

Large-scale, broad outflows are common in active galaxies. In systems where star formation coexists with an AGN, it is unclear yet the role that both play on driving the outflows. In this work we present three-dimensional radiative-cooling MHD simulations of the formation of these outflows, considering the feedback from both the AGN and supernovae-driven winds. We find that a large-opening-angle AGN wind develops fountain structures that make the expanding gas to fall back. Furthermore, it exhausts the gas near the nuclear region, extinguishing star formation and accretion within a few 100.000 yr, which establishes the duty cycle of these outflows. The AGN wind accounts for the highest speed features in the outflow with velocities around 10.000 km s$^{-1}$ (as observed in UFOs), but these are not as cold and dense as required by observations of molecular outflows. The SNe-driven wind is the main responsible for the observed mass-loading of the outflows.


arXiv:1809.07598v1 [pdf, other]
The Serpens filament: at the onset of slightly supercritical collapse
Comments: 22 pages, 14 figures, 4 tables, accepted for publication in A&A; for the draft showing figures with full resolution, see http://gongyan2444.github.io/pdf/absfil.pdf

The Serpens filament, as one of the nearest infrared dark clouds, is regarded as a pristine filament at a very early evolutionary stage of star formation. In order to study its molecular content and dynamical state, we mapped this filament in seven species. Among them, HCO$^{+}$, HNC, HCN, and CS show self-absorption, while C$^{18}$O is most sensitive to the filamentary structure. A kinematic analysis demonstrates that this filament forms a velocity-coherent (trans-)sonic structure, a large part of which is one of the most quiescent regions in the Serpens cloud. Widespread C$^{18}$O depletion is found throughout the Serpens filament. Based on the Herschel dust-derived H$_{2}$ column density map, the line mass of the filament is 36--41~M$_{\odot}$~pc$^{-1}$, and its full width at half maximum is 0.17$\pm$0.01~pc, while its length is ~1.6~pc. The inner radial column density profile of this filament can be well fitted with a Plummer profile with an exponent of 2.2$\pm$0.1, a scale radius of $0.018\pm 0.003$ pc, and a central density of $(4.0\pm 0.8)\times 10^{4}$~cm$^{-3}$. The Serpens filament appears to be slightly supercritical. The widespread blue-skewed HNC and CS line profiles and HCN hyperfine line anomalies across this filament indicate radial infall in parts of the Serpens filament. C$^{18}$O velocity gradients also indicate accretion flows along the filament. The velocity and density structures suggest that such accretion flows are likely due to a longitudinal collapse parallel to the filament's long axis. Both the radial infall rate and the longitudinal accretion rate along the Serpens filament are lower than all previously reported values in other filaments. This indicates that the Serpens filament lies at an early evolutionary stage when collapse has just begun, or that thermal and non-thermal support are effective in providing support against gravity.


arXiv:1809.07601v1 [pdf, other]
A Monte Carlo based simulation of the galactic chemical evolution of the Milky Way galaxy
Comments: Accepted in "Monthly Notices of the Royal Astronomical Society", 65 pages, 10 figures in main text + supp. data

The formation and chemical evolution of the Milky Way Galaxy is numerically simulated by developing a Monte Carlo approach to predict the elemental abundance gradients and other galactic features using the revised solar abundance. The galaxy is accreted gradually by using either a two-infall or a three-infall accretion scenario. The galaxy is chemically enriched by the nucleosynthetic contributions from an evolving ensemble of generations of stars. We analyse the role of star formation efficiency. The influence of the radial gas inflow as well as radial gas mixing on the evolution of galaxy is also studied. The SN Ia delay time distribution (DTD) is incorporated by synthesizing SN Ia populations using random numbers based on a distribution function. The elemental abundance evolutionary trends corroborate fractional contributions of ~0.1 from prompt ( < 100 Myr) SN Ia population. The models predict steep gradients in the inner regions and less steep gradients in the outer regions which agrees with the observations. The gradients indicate an average radial gas mixing velocity of < 1 km/s. The models with radial gas inflows reproduce the observed inversion in the elemental abundance gradients around 2 billion years. The three-infall accretion scenario performs better than the two-infall accretion model in terms of explaining the elemental abundance distributions of the galactic halo, thick and thin discs. The accuracy of all the models has been monitored as a cumulative error of < 0.15 M in the mass balance calculations during the entire evolution of the galaxy.


arXiv:1809.07604v1 [pdf, other]
The bright-end galaxy candidates at z ~ 9 from 79 independent HST fields
Comments: 18pages, 7figures, 6tables. Submitted to AAS journal

We present a full data analysis of the Brightest of Reionizing Galaxies Survey (BoRG[z9]) pure-parallel HST imaging observations in Cycle 22. The medium deep exposures with five HST/WFC3IR+UVIS filter bands from 79 independent sightlines (~370 arcmin^2) provide the least biased determination of number density for z>9 bright galaxies against cosmic variance. After a strict two-step selection for candidate galaxies, including dropout color and photometric redshift analyses, and revision of previous BoRG candidates, we identify 1 source at z~10 and 2 sources at z~9. The z~10 candidate shows evidence of line-of-sight lens magnification (mu~1.5), yet it appears surprisingly luminous (MUV ~ -22.6\pm0.3 mag), making it one of the brightest candidates at z > 8 known (~ 0.3 mag brighter than the z = 8.68 galaxy EGSY8p7, spectroscopically confirmed by Zitrin and collaborators). For z ~ 9 candidates, we include previous data points at fainter magnitudes and find that the data is well fitted by a Schechter luminosity function with alpha ~ -2.1, MUV ~ -21.5 mag, and log phi ~ -4.5 Mpc^-3mag^-1, for the first time without fixing any parameters. The inferred cosmic star formation rate density is consistent with non-accelerated evolution from lower redshift.


arXiv:1809.07627v1 [pdf, other]
The star formation history and metallicity in the galactic inner bulge revealed by the red giant branch bump
Comments: Accepted for publication in A&A

The study of the inner region of the Milky Way's bulge is hampered by high interstellar extinction and extreme source crowding. Sensitive high angular resolution near-infrared imaging is needed to study stellar populations in such a complex environment. We use the 0.2$''$ angular resolution $JHK_s$ data from the GALACTICNUCLEUS survey to study the stellar population within two $8.0'\times 3.4'$ fields, about 0.6$^\circ$ and 0.4$^\circ$ to the Galactic north of the Milky Way's centre and to compare it with one in the immediate surroundings of Sagittarius A*. We also characterise the extinction curve of the two fields. The average interstellar extinction to the outer and the inner field is $A_{K_s} \sim 1.20 \pm 0.08$ mag and $\sim 1.48 \pm 0.10$ mag, respectively. We present $K_{s}$ luminosity functions that are complete down to at least 2 mag below the red clump (RC). We detect a feature in the luminosity functions that is fainter than the RC by $0.80\pm0.03$ and $0.79\pm0.02$ mag, respectively, in the $K_s$-band. It runs parallel to the reddening vector. We identify the feature as the red giant branch bump. Fitting $\alpha$-enhanced BaSTI luminosity functions to our data, we find that a single old stellar population of $\sim12.8 \pm 0.6$ Gyr and $Z = 0.040 \pm 0.003$ provides the best fit. We obtain that the stellar population in the innermost bulge is old, similar to the one at larger distances from the Galactic plane, and that its metallicity increases down to distances as short as about 60 pc from the centre of the Milky Way. Comparing it with previous known values at larger latitudes ($|b|>2^\circ$), our results favour a flattening of the gradient at $|b|<2^\circ$. As a secondary result we obtain that the extinction index in the studied regions agrees the value of $\alpha = 2.30\pm0.08$, derived in Nogueras-Lara et al. 2018 for the very Galactic centre.


arXiv:1809.07650v1 [pdf, other]
The WAGGS project - II. The reliability of the calcium triplet as a metallicity indicator in integrated stellar light
Comments: 33 pages, 27 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Society

Using data from the WiFeS Atlas of Galactic Globular cluster Spectra we study the behaviour of the calcium triplet (CaT), a popular metallicity indicator in extragalactic stellar population studies. A major caveat of these studies is that the potential sensitivity to other stellar population parameters such as age, calcium abundance and the initial mass function has not yet been empirically evaluated. Here we present measurements of the strength of the CaT feature for 113 globular clusters in the Milky Way and its satellite galaxies. We derive empirical calibrations between the CaT index and both the iron abundance ([Fe/H]) and calcium abundance ([Ca/H]), finding a tighter relationship for [Ca/H] than for [Fe/H]. For stellar populations 3 Gyr and older the CaT can be used to reliably measure [Ca/H] at the 0.1 dex level but becomes less reliable for ages of $\sim 2$ Gyr and younger. We find that the CaT is relatively insensitive to the horizontal branch morphology. The stellar mass function however affects the CaT strengths significantly only at low metallicities. Using our newly derived empirical calibration, we convert our measured CaT indices into [Ca/H] values for the globular clusters in our sample.


arXiv:1809.07654v1 [pdf, other]
Constraining the Solar Galactic Reflex Velocity Using Gaia Observations of the Sagittarius Stream
Comments: 7 pages, 3 figures. Submitted to The Astrophysical Journal Letters

Because of its particular orientation around the Galaxy - i.e., in a plane nearly perpendicular to the Galactic plane and containing both the Sun and Galactic center - the Sagittarius (Sgr) stream provides a powerful means by which to measure the solar reflex velocity, and thereby infer the velocity of the Local Standard of Rest (LSR), in a way that is independent of assumptions about the solar Galactocentric distance. Moreover, the solar reflex velocity with respect to the stream is projected almost entirely into the proper motion component of Sgr stream stars perpendicular to the Sgr plane, which makes the inferred velocity relatively immune to most Sgr model assumptions. Using Gaia DR2 proper motions of ~2,000 stars identified to be Sgr stream candidates in concert with the Law and Majewski (2010) Sgr N-body models (which provide a good match to the Gaia observations) we constrain the solar reflex velocity induced by its orbital motion around the Galaxy to be $\Theta_{\odot} = 253 \pm 6$ km/s. Assuming a solar peculiar motion in the direction of orbital rotation of 12 km/s, and an LSR velocity of 12 km/s with respect to the local circular speed, the implied circular speed of the Milky Way at the solar circle is $229 \pm 6$ km/s.


arXiv:1809.07673v1 [pdf, other]
Relaxation in a Fuzzy Dark Matter Halo
Comments: 23 pages, 7 figures

Dark matter may be composed of light bosons, ${m_b \sim 10^{-22}\, \mathrm{eV}}$, with a de Broglie wavelength $\lambda \sim 1 \,\mathrm{kpc}$ in typical galactic potentials. Such 'fuzzy' dark matter (FDM) behaves like cold dark matter (CDM) on much larger scales than the de Broglie wavelength, but may resolve some of the challenges faced by CDM in explaining the properties of galaxies on small scales ($\lesssim 10 \mathrm{kpc}$). Because of its wave nature, FDM exhibits stochastic density fluctuations on the scale of the de Broglie wavelength that never damp. The gravitational field from these fluctuations scatters stars and black holes, causing their orbits to diffuse through phase space. We show that this relaxation process can be analyzed quantitatively with the same tools used to analyze classical two-body relaxation in an $N$-body system, and can be described by treating the FDM fluctuations as quasiparticles, with effective mass $\sim 10^7 M_\odot {(1\,\mathrm{kpc}/r)}^2{(10^{-22}\,\mathrm{eV}/m_b)}^3$ in a galaxy with a constant circular speed of $200\,\mathrm{kms}$. This novel relaxation mechanism may stall the inspiral of supermassive black holes or globular clusters due to dynamical friction at radii of a few hundred pc, and can heat and expand the central regions of galaxies. These processes can be used to constrain the mass of the light bosons that might comprise FDM.


arXiv:1809.07675v1 [pdf, other]
Slow-then-rapid quenching as traced by enhanced metallicities of cluster galaxies at z~0.2 in the slow quenching phase
Comments: 11 pages, 7 figures; submitted on 20 Sep 2018 to A&A

(Abridged) We explore 7 clusters from LoCuSS at z~0.2 with spectra of ~2700 cluster members from the ACReS Hectospec survey covering a region which corresponds to about three virial radii for each cluster. We measure fluxes of five emission lines of cluster members enabling us to unambiguously derive O/H gas metallicities, and also SFRs from extinction corrected Halpha fluxes. We compare our cluster galaxy sample with a field sample of ~1000 galaxies at similar redshifts observed with Hectospec. We find that star-forming cluster and field galaxies show similar median specific SFRs in a given mass bin, but their O/H values are displaced to higher values at projected radii of R<R200 compared with galaxies at larger radii and in the field. The comparison with metallicity-SFR-mass model predictions with inflowing gas indicates a slow-quenching scenario in which strangulation is initiated when galaxies pass R~R200 by stopping the inflow of gas. The metallicities of cluster members inside R200 are thereby increasing, but their SFRs are hardly affected for a period of time, because these galaxies consume available disk gas. We use the fraction of star-forming cluster galaxies as a function of clustercentric radius compared to predictions from the Millennium simulation to constrain quenching timescales to be 1-2Gyrs. This is consistent with a slow-then-rapid quenching scenario. Slow quenching (strangulation) starts when the gas inflow is stopped when the galaxy passes R200 with a phase in which cluster galaxies are still star-forming, but they show elevated metallicities tracing the ongoing quenching. This phase lasts for 1-2Gyrs, meanwhile the galaxies travel to denser inner regions of the cluster, and is followed by a "rapid" phase: a rapid complete quenching of star formation due to the increasing ram-pressure towards the cluster center which can also strip the cold gas in massive galaxies.


arXiv:1809.07709v1 [pdf, other]
A low-density hot Jupiter in a near-aligned, 4.5-day orbit around a $V$ = 10.8, F5V star
Comments: Submitted to AJ. 9 pages, 6 figures, 5 tables

We report the independent discovery and characterisation of a hot Jupiter in a 4.5-d, transiting orbit around the star TYC 7282-1298-1 ($V$ = 10.8, F5V). The planet has been pursued by the NGTS team as NGTS-2b and by ourselves as WASP-179b. We characterised the system using a combination of photometry from WASP-South and TRAPPIST-South, and spectra from CORALIE (around the orbit) and HARPS (through the transit). We find the planet's orbit to be nearly aligned with its star's spin. From a detection of the Rossiter-McLaughlin effect, we measure a projected stellar obliquity of $\lambda = -19 \pm 6^\circ$. From line-profile tomography of the same spectra, we measure $\lambda = -11 \pm 5^\circ$. We find the planet to have a low density ($M_{\rm P}$ = 0.67 $\pm$ 0.09 $M_{\rm Jup}$, $R_{\rm P}$ = 1.54 $\pm$ 0.06 $R_{\rm Jup}$), which, along with its moderately bright host star, makes it a good target for transmission spectroscopy. We find a lower stellar mass ($M_*$ = $1.30 \pm 0.07$ $M_\odot$) than reported by the NGTS team ($M_*$ = $1.64 \pm 0.21$ $M_\odot$), though the difference is only $1.5$ $\sigma$.


arXiv:1809.07710v1 [pdf, other]
Probing the High-Redshift Universe with SPICA: Toward the Epoch of Reionization and Beyond
Comments: 24 pages, 8 figures, submitted to PASA (SPICA special issue), revised version after the first referee report (comments still welcome)

With the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z>5 that are hyper-luminous in the infrared ($\mu$$L_{\rm IR}>10^{13}$ L$_{\odot}$, where $\mu$ is a lensing magnification factor), the possibility has opened up for SPICA, the proposed ESA M5 mid-/far-infrared mission, to extend its spectroscopic studies toward the epoch of reionization and beyond. In this paper, we examine the feasibility and scientific potential of such observations with SPICA's far-infrared spectrometer SAFARI, which will probe a spectral range (35-230 $\mu$m) that will be unexplored by ALMA and JWST. Our simulations show that SAFARI is capable of delivering good-quality spectra for hyper-luminous infrared galaxies (HyLIRGs) at z=5-10, allowing us to sample spectral features in the rest-frame mid-infrared and to investigate a host of key scientific issues, such as the relative importance of star formation versus AGN, the hardness of the radiation field, the level of chemical enrichment, and the properties of the molecular gas. From a broader perspective, SAFARI offers the potential to open up a new frontier in the study of the early Universe, providing access to uniquely powerful spectral features for probing first-generation objects, such as the key cooling lines of low-metallicity or metal-free forming galaxies (fine-structure and H2 lines) and emission features of solid compounds freshly synthesized by Population III supernovae. Ultimately, SAFARI's ability to explore the high-redshift Universe will be determined by the availability of sufficiently bright targets (whether intrinsically luminous or gravitationally lensed). With its launch expected around 2030, SPICA is ideally positioned to take full advantage of upcoming wide-field surveys such as LSST, SKA, Euclid, and WFIRST, which are likely to provide extraordinary targets for SAFARI.


arXiv:1809.07713v1 [pdf, other]
Nonlinear evolution of initially biased tracers in modified gravity
Comments: 38 pages, 8 figures

In this work we extend the perturbation theory for modified gravity (MG) in two main aspects. First, the construction of matter overdensities from Lagrangian displacement fields is shown to hold in a general framework, allowing us to find Standard Perturbation Theory (SPT) kernels from known Lagrangian Perturbation Theory (LPT) kernels. We then develop a theory of biased tracers for generalized cosmologies, extending already existing formalisms for $\Lambda$CDM. We present the correlation function in Convolution-LPT and the power spectrum in SPT for $\Lambda$CDM, $f(R)$ Hu-Sawicky, and DGP braneworld models. Our formalism can be applied to many generalized cosmologies and to facilitate it, we are making public a code to compute these statistics. We further study the relaxation of bias with the use of a simple model and of excursion set theory, showing that in general the bias parameters have smaller values in MG than in General Relativity.


arXiv:1809.07715v1 [pdf, other]
Rotational Temperature Modeling of the Swan $Δν= 0$ Band Sequence in Comet 122P/de~Vico
Comments: This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Journal of Physical Chemistry, Part A:Isolated Molecules, Clusters, Radicals, and Ions; Environmental Chemistry, Geochemistry, and Astrochemistry; New Tools and Methods, copyright American Chemical Society after peer review

We modeled observations of the C$_2$ $\mathrm{d} ^3\Pi_g - \mathrm{a} ^3\Pi_u$ (Swan) $\Delta \nu = 0$ sequence observed in spectra of comet 122P/de Vico obtained with the 2.7m Harlan J. Smith Telescope and Tull Coude spectrograph of McDonald observatory on 10/03/1995 and 10/04/1995. The data used spanned 4986-5169\AA at R=$\lambda/\Delta\lambda$=60,000. We used the PGOPHER molecular spectra model to generate and fit synthetic spectra with the d$^3\Pi_g$ having one and two rotational temperatures. We found the excited state had a two component rotational temperature, similar to that found for comet Halley. The modeled spectrum was sufficiently high quality that local perturbations were important to include. The large perturbation, b$^3\Sigma_g^-(\nu=10)$, was added to our fits and some new estimates on its molecular constants were found.


arXiv:1809.07737v1 [pdf, other]
Constraining the kinetically dominated Universe
Comments: Submitted to Physical Review D, 15 pages, 12 figures, 1 table

We present cosmological constraints from Planck 2015 data for a universe that is kinetically dominated at very early times. We perform a Markov chain Monte Carlo analysis to estimate parameters and use nested sampling to determine the evidence for a model comparison of the single-field quadratic and Starobinsky inflationary models with the standard $\Lambda$CDM cosmology. In particular we investigate how different amounts of inflation before and after horizon exit affect the primordial power spectrum and subsequently the power spectrum of the cosmic microwave background. We find that the model using kinetically dominated initial conditions for inflation performs similarly well in terms of Bayesian evidence as a model directly starting out in the slow-roll phase, despite having an additional parameter. The data show a slight preference for a cutoff at large scales in the primordial and temperature power spectra.


arXiv:1809.07746v1 [pdf, other]
Outliers: multicolour photometry guiding the search for evolved binary systems in the globular cluster 47 Tucanae
Comments: 13 pages, 8 figures, 2 tables. Accepted for publication in MNRAS on September 18, 2018

We use Hubble Space Telescope multicolour photometry of the globular cluster 47 Tucanae to uncover a population of 24 objects with no previous classification that are outliers from the single-star model tracks in the colour-magnitude diagram and yet are likely cluster members. By comparing those sources with evolutionary models and X-ray source catalogues, we were able to show that the majority of those sources are likely binary systems that do not have any X-ray source detected nearby, most possibly formed by a white dwarf and a main-sequence star and a small number of possible double-degenerate systems.


arXiv:1809.07758v1 [pdf, other]
The properties of the kinematically distinct components in NGC 448 and NGC 4365
Comments: 14 pages, 12 figures, to appear in A&A

Aims. We study the kinematically distinct components in two early-type galaxies NGC 448 and NGC 4365 aided by integral-field observations with the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope. We aim to measure the brightness profiles, kinematics, and stellar population properties of the peculiar kinematic structures in these galaxies and shed light on their true nature and formation mechanism. Methods. We use a kinematic decomposition technique to separate the individual contributions to the spectra of the two distinct kinematic components observed at each spatial position in the field of view. By folding back the outcome of a photometric decomposition we reduce the intrinsic degeneracies in recovering the kinematics and the best-fitting stellar spectral templates. Finally, by extracting the Lick line-strength indices for the individual components and fitting them to single stellar population models we derive their ages, metallicities, and {\alpha}/Fe overabundances. Results. The two kinematically decoupled stellar components in NGC 448 have similar ages, but different chemical compositions. The distinct kinematic feature in NGC 448 has a nearly exponential surface-brightness light profile, dominates in the innermost ~ 10", is smaller in size, and is very likely an embedded counter-rotating disk as also indicated by its kinematics. It has higher metallicity than the main galaxy stellar body and lower {\alpha}/Fe overabundance. By contrast, we do not find evidence for true decoupling in the two distinct kinematic components in NGC 4365. This confirms earlier work suggesting that the kinematically distinct core is likely not a separate dynamical structure, but most certainly likely a projection effect stemming from the orbital structure of this galaxy that was previously found to be intrinsically triaxial in shape.