Z. Kostrzewa-Rutkowska; P. G. Jonker; S. T. Hodgkin; D. Eappachen; D. L. Harrison; S. E. Koposov; G. Rixon; Ł. Wyrzykowski; A. Yoldaş; E. Breedt; A. Delgado; M. van Leeuwen; T. Wevers; P. W. Burgess; F. De Angeli; D. W. Evans; P. Osborne; M. Riello
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT The recent discoveries of gravitational wave events and in one case also its electromagnetic (EM) counterpart allow us to study the Universe in a novel way. The increased sensitivity of the LIGO and Virgo detectors has opened the possibility for regular detections of EM transient events from mergers of stellar remnants. Gravitational wave sources are expected to have sky localization up to a few hundred square degrees, thus Gaia as an all-sky multi-epoch photometric survey has the potential to be a good tool to search for the EM counterparts. In this paper, we study the possibility of detecting EM counterparts to gravitational wave sources using the Gaia Science Alerts system. We develop an extension to current used algorithms to find transients and test its capabilities in discovering candidate transients on a sample of events from the observation periods O1 and O2 of LIGO and Virgo. For the gravitational wave events from the current run O3, we expect that about 16 (25) per cent should fall in sky regions observed by Gaia 7 (10) d after gravitational wave. The new algorithm will provide about 21 candidates per day from the whole sky.
M. Cappetta; R. P. Saglia; Jayne Birkby; J. Koppenhoefer; D. J. Pinfield; S. T. Hodgkin; P. Cruz; G. Kovács; Brigitta Sipőcz; D. Barrado; B. Nefs; Ya. V. Pavlenko; L. Fossati; C. del Burgo; E. L. Martı́n; I. A. G. Snellen; J. R. Barnes; David A. Campbell; S. Catalán; M. C. Gálvez-Ortiz; N. Goulding; C. A. Haswell; O. Ivanyuk; H. R. A. Jones; M. K. Kuznetsov; N. Lodieu; Federico Marocco; D. Mislis; F. Murgas; R. Napiwotzki; Ε. Πάλλη; D. Pollacco; L Sarro Baro; E. Solano; P. R. Steele; H. Stoev; R. Tata; J. Zendejas
Monthly Notices of the Royal Astronomical Society · DOI
<p>This is a correction to: </p><div><a href="https://academic.oup.com/mnras/article/427/3/1877/1094173"><u>… Notices of the Royal Astronomical Society</em>, Volume 427, Issue 3, December 2012, Pages 1877–1890, </u></a><a href="https://doi.org/10.1111/j.1365-2966.2012.21937.x"><u>https://d…;
M. Riello; F. De Angeli; D. W. Evans; P. Montegriffo; J. M. Carrasco; G. Busso; L. Palaversa; P. W. Burgess; C. Diener; M. Davidson; N. Rowell; C. Fabricius; C. Jordi; M. Bellazzini; E. Pancino; D. L. Harrison; C. Cacciari; F. van Leeuwen; N. C. Hambly; S. T. Hodgkin; P. Osborne; G. Altavilla; M. A. Barstow; Brown, AGA; M. Castellani; S. Cowell; F. De Luise; G. Gilmore; G. Giuffrida; S. L. Hidalgo; G. Holland; S. Marinoni; C. Pagani; A. M. Piersimoni; L. Pulone; S. Ragaini; M. Rainer; P. J. Richards; N. Sanna; N. A. Walton; M. Weiler; A. Yoldaş
arXiv (Cornell University) · DOI
Context. Gaia Early Data Release 3 ( Gaia EDR3) contains astrometry and photometry results for about 1.8 billion sources based on observations collected by the European Space Agency Gaia satellite during the first 34 months of its operational phase. Aims. In this paper, we focus on the photometric content, describing the input data, the algorithms, the processing, and the validation of the results. Particular attention is given to the quality of the data and to a number of features that users may need to take into account to make the best use of the Gaia EDR3 catalogue. Methods. The processing broadly followed the same procedure as for Gaia DR2, but with significant improvements in several aspects of the blue and red photometer (BP and RP) preprocessing and in the photometric calibration process. In particular, the treatment of the BP and RP background has been updated to include a better estimation of the local background, and the detection of crowding effects has been used to exclude affected data from the calibrations. The photometric calibration models have also been updated to account for flux loss over the whole magnitude range. Significant improvements in the modelling and calibration of the Gaia point and line spread functions have also helped to reduce a number of instrumental effects that were still present in DR2. Results. Gaia EDR3 contains 1.806 billion sources with G -band photometry and 1.540 billion sources with G BP and G RP photometry. The median uncertainty in the G -band photometry, as measured from the standard deviation of the internally calibrated mean photometry for a given source, is 0.2 mmag at magnitude G = 10–14, 0.8 mmag at G ≈ 17, and 2.6 mmag at G ≈ 19. The significant magnitude term found in the Gaia DR2 photometry is no longer visible, and overall there are no trends larger than 1 mmag mag −1 . Using one passband over the whole colour and magnitude range leaves no systematics above the 1% level in magnitude in any of the bands, and a larger systematic is present for a very small sample of bright and blue sources. A detailed description of the residual systematic effects is provided. Overall the quality of the calibrated mean photometry in Gaia EDR3 is superior with respect to DR2 for all bands.
N. Rowell; M. Davidson; L. Lindegren; F. van Leeuwen; J. Castañeda; C. Fabricius; U. Bastian; N. C. Hambly; J. Hernández; A. Bombrun; D. W. Evans; F. De Angeli; M. Riello; D. Busonero; C. Crowley; A. Mora; U. Lammers; G. Gracia; J. Portell; M. Biermann; A. G. A. Brown
arXiv (Cornell University) · DOI
Context: The unprecedented astrometric precision of the Gaia mission relies on accurate estimates of the locations of sources in the Gaia data stream. This is ultimately performed by point spread function (PSF) fitting, which in turn requires an accurate reconstruction of the PSF. Gaia Early Data Release 3 (EDR3) will, for the first time, use a PSF calibration that models several of the strongest dependences, leading to signficantly reduced systematic errors. Aims: We describe the PSF model and calibration pipeline implemented for Gaia EDR3, including an analysis of the calibration results over the 34 months of data. We include a discussion of the limitations of the current pipeline and directions for future releases. This will be of use both to users of Gaia data and as a reference for other precision astrometry missions. Methods: We develop models of the 1D line spread function (LSF) and 2D PSF profiles based on a linear combination of basis components. We fit the models to selected primary sources in independent time ranges, using simple parameterisations for the colour and other dependences. Variation in time is smoothed by merging the independent calibrations in a square root information filter, with resets at certain mission events that induce a discontinuous change in the PSF. Results: The PSF calibration shows strong time and colour dependences that accurately reproduce the varying state of the Gaia astrometric instrument. Analysis of the residuals reveals both the performance and the limitations of the current models and calibration pipeline, and indicates the directions for future development. Conclusions: The PSF modelling and calibration carried out for Gaia EDR3 represents a major step forwards in the data processing and will lead to reduced systematic errors in the core mission data products. Further significant improvements are expected in the future data releases.
Jaroslav Merc; J. Mikołajewska; M. Gromadzki; C. Gałan; Krystian Iłkiewicz; J. Skowron; Ł. Wyrzykowski; S. T. Hodgkin; Krzysztof A. Rybicki; Paweł Zieliński; K. Kruszyńska; V. Godunova; A. Simon; V. Reshetnyk; Fraser Lewis; U. Kolb; M. Morrell; A. J. Norton; Supachai Awiphan; S. Poshyachinda; D. E. Reichart; M. Greet; J. Kolgjini
Astronomy and Astrophysics · DOI
Context. Besides the astrometric mission of the Gaia satellite, its repeated and high-precision measurements also serve as an all-sky photometric transient survey. The sudden brightenings of the sources are published as Gaia Photometric Science Alerts and are made publicly available, allowing the community to photometrically and spectroscopically follow up on the object. Aims. The goal of this paper is to analyze the nature and derive the basic parameters of Gaia18aen, a transient detected at the beginning of 2018. This object coincides with the position of the emission-line star WRAY 15-136. The brightening was classified as a “nova?” on the basis of a subsequent spectroscopic observation. Methods. We analyzed two spectra of Gaia18aen and collected the available photometry of the object covering the brightenings in 2018 and also the preceding and following periods of quiescence. Based on this observational data, we derived the parameters of Gaia18aen and discussed the nature of the object. Results. Gaia18aen is the first symbiotic star discovered by Gaia satellite. The system is an S-type symbiotic star and consists of an M giant of a slightly super-solar metallicity, where T eff ∼ 3500 K, a radius of ∼230 R ⊙ , and a high luminosity L ∼ 7400 L ⊙ . The hot component is a hot white dwarf. We tentatively determined the orbital period of the system ∼487 d. The main outburst of Gaia18aen in 2018 was accompanied by a decrease in the temperature of the hot component. The first phase of the outburst was characterized by the high luminosity L ∼ 27 000 L ⊙ , which remained constant for about three weeks after the optical maximum, later followed by the gradual decline of luminosity and increase of temperature. Several re-brightenings have been detected on the timescales of hundreds of days.
Romain Lucchesi; C. Lardo; F. Primas; P. Jablonka; P. North; G. Battaglia; Else Starkenburg; V. Hill; M. J. Irwin; P. François; Matthew Shetrone; Eline Tolstoy; Kim A. Venn
Springer Link (Chiba Institute of Technology) · DOI
We present the high-resolution spectroscopic analysis of two new extremely metal-poor star (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were preselected from medium-resolution spectra centered around the Ca <ns0:sc>II</ns0:sc> triplet in the near-infrared and were followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H] = −2.95 and [Fe/H] = −3.01, which place them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the α, Fe-peak, and neutron-capture elements, are determined. In particular, we present the first unambiguous detection of Zn in a classical dwarf at extremely low metallicity. Previous indications were made of a large scatter in the abundance ratios of the Sextans stellar population around [Fe/H] ∼ − 3 when compared to other galaxies, particularly with very low observed [α/Fe] ratios. We took the opportunity of reanalyzing the full sample of EMPS in Sextans and find a [α/Fe] Milky Way-like plateau and a ∼0.2 dex dispersion at fixed metallicity.
M. Monguió; R. Greimel; J. E. Drew; Geert Barentsen; P. Groot; M. J. Irwin; J. Casares; B. T. Gänsicke; Philip J. Carter; J. M. Corral-Santana; N. P. Gentile-Fusillo; S. Greiss; L. M. van Haaften; Mark Hollands; David Jones; Thomas Kupfer; Christopher J. Manser; D. N. A. Murphy; Anna F. McLeod; T. Oosting; Q. A. Parker; S. Pyrzas; P. Rodríguez-Gil; Jan van Roestel; Simone Scaringi; P. Schellart; Odette Toloza; O. Văduvescu; L. van Spaandonk; K. Verbeek; N. J. Wright; J. Eislöffel; J. Fabregat; A. Harris; R. A. H. Morris; S. Phillipps; R. Raddi; L. Sabin; Y. C. Unruh; J. S. Vink; R. Wesson; A. Cardwell; A. de Burgos; R. K. Cochrane; Saeed Doostmohammadi; Teo Močnik; H. Stoev; L. Suárez-Andrés; Vlad Tudor; T. G. Wilson; Tarik Zegmott
Astronomy and Astrophysics · DOI
The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i , r , narrow-band H α , g , and U RGO . The IGAPS footprint fills the Galactic coordinate range, | b | &lt; 5° and 30° &lt; ℓ &lt; 215°. A uniform calibration, referred to as the Pan-STARRS system, is applied to g , r , and i , while the H α calibration is linked to r and then is reconciled via field overlaps. The astrometry in all five bands has been recalculated in the reference frame of Gaia Data Release 2. Down to i ∼ 20 mag (Vega system), most stars are also detected in g , r , and H α . As exposures in the r band were obtained in both the IPHAS and UVEX surveys, typically a few years apart, the catalogue includes two distinct r measures, r I and r U . The r 10 σ limiting magnitude is approximately 21, with median seeing of 1.1 arcsec. Between approximately 13th and 19th mag in all bands, the photometry is internally reproducible to within 0.02 mag. Stars brighter than r = 19.5 mag are tested for narrow-band H α excess signalling line emission, and for variation exceeding | r I − r U | = 0.2 mag. We find and flag 8292 candidate emission line stars and over 53 000 variables (both at &gt; 5 σ confidence).
Laura K. Rogers; Siyi Xu; Amy Bonsor; S. T. Hodgkin; K. Y. L. Su; Ted von Hippel; Michael Jura
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT The inwards scattering of planetesimals towards white dwarfs is expected to be a stochastic process with variability on human time-scales. The planetesimals tidally disrupt at the Roche radius, producing dusty debris detectable as excess infrared emission. When sufficiently close to the white dwarf, this debris sublimates and accretes on to the white dwarf and pollutes its atmosphere. Studying this infrared emission around polluted white dwarfs can reveal how this planetary material arrives in their atmospheres. We report a near-infrared monitoring campaign of 34 white dwarfs with infrared excesses with the aim to search for variability in the dust emission. Time series photometry of these white dwarfs from the United Kingdom Infrared Telescope (Wide Field Camera) in the J-, H-, and K-bands was obtained over baselines of up to 3 yr. We find no statistically significant variation in the dust emission in all three near-infrared bands. Specifically, we can rule out variability at ∼1.3 per cent for the 13 white dwarfs brighter than 16th mag in K-band, and at ∼10 per cent for the 32 white dwarfs brighter than 18th mag over time-scales of 3 yr. Although to date two white dwarfs, SDSS J095904.69−020047.6 and WD 1226+110, have shown K-band variability, in our sample we see no evidence of new K-band variability at these levels. One interpretation is that the tidal disruption events that lead to large variabilities are rare occur on short time-scales, and after a few years the white dwarfs return to being stable in the near-infrared.
Z. Kostrzewa-Rutkowska; P. G. Jonker; S. T. Hodgkin; D. Eappachen; D. L. Harrison; S. E. Koposov
Monthly Notices of the Royal Astronomical Society · DOI
\n Contains fulltext :\n 219281.pdf (Publisher’s version ) (Open Access)\n
N. Blagorodnova; V Karambelkar; S. M. Adams; M. M. Kasliwal; C. S. Kochanek; Subo Dong; H. Campbell; S. T. Hodgkin; J. Jencson; J. Johansson; S. Kozłowski; Russ R. Laher; Frank J. Masci; P. Nugent; Umaa Rebbapragada
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT M31-LRN-2015 is a likely stellar merger discovered in the Andromeda Galaxy in 2015. We present new optical to mid-infrared photometry and optical spectroscopy for this event. Archival data show that the source started to brighten ∼2 yr before the nova event. During this precursor phase, the source brightened by ∼3 mag. The light curve at 6 and 1.5 months before the main outburst may show periodicity, with periods of 16 ± 0.3 and 28.1 ± 1.4 d, respectively. This complex emission may be explained by runaway mass-loss from the system after the binary undergoes Roche lobe overflow, leading the system to coalesce in tens of orbital periods. While the progenitor spectral energy distribution shows no evidence of pre-existing warm dust in the system, the remnant forms an optically thick dust shell at approximately four months after the outburst peak. The optical depth of the shell increases dramatically after 1.5 yr, suggesting the existence of shocks that enhance the dust formation process. We propose that the merger remnant is likely an inflated giant obscured by a cooling shell of gas with mass ∼0.2 M⊙ ejected at the onset of the common envelope phase.
G. M. Seabroke; M. Cropper; Baker, Steven; K. Benson; Dolding, Chris; M. Smith; Arancha Delgado; S. T. Hodgkin; D. L. Harrison; Guy Rixon; Ł. Wyrzykowski
arXiv (Cornell University) · DOI
Gaia Photometric Science Alerts (GPSA) publishes Gaia G magnitudes and Blue Photometer (BP) and Red Photometer (RP) low-resolution epoch spectra of transient events. 27 high-resolution spectra from Gaia's Radial Velocity Spectrometer (RVS) of 12 GPSAs have also been published. These 27 RVS epoch spectra are presented next to their corresponding BP and RP epoch spectra in a single place for the first time. We also present one new RVS spectrum of a 13th GPSA that could not be published by the GPSA system. Of the 13 GPSA with RVS spectra, five are photometrically classified as unknown, five as supernovae (three as SN Ia, one as SN II, one as SN IIP), one as a cataclysmic variable, one as a binary microlensing event and one as a young stellar object. The five GPSAs classified as unknown are potential scientific opportunities, while all of them are a preview of the epoch RVS spectra that will be published in Gaia's fourth data release.
N. Chornay; N. A. Walton
Astronomy and Astrophysics · DOI
Context. Accurate distance measurements are fundamental to the study of planetary nebulae (PNe) but they have long been elusive. The most accurate and model-independent distance measurements for galactic PNe come from the trigonometric parallaxes of their central stars, which were only available for a few tens of objects prior to the Gaia mission. Aims. The accurate identification of PN central stars in the Gaia source catalogues is a critical prerequisite for leveraging the unprecedented scope and precision of the trigonometric parallaxes measured by Gaia . Our aim is to build a complete sample of PN central star detections with minimal contamination. Methods. We developed and applied an automated technique based on the likelihood ratio method to match candidate central stars in Gaia Data Release 2 (DR2) to known PNe in the Hong Kong/AAO/Strasbourg H α PN catalogue, taking into account the BP – RP colours of the Gaia sources as well as their positional offsets from the nebula centres. These parameter distributions for both true central stars and background sources were inferred directly from the data. Results. We present a catalogue of over 1000 Gaia sources that our method has automatically identified as likely PN central stars. We demonstrate how the best matches enable us to trace nebula and central star evolution and to validate existing statistical distance scales, and we discuss the prospects for further refinement of the matching based on additional data. We also compare the accuracy of our catalogue to that of previous works.
Romaine Theler; P. Jablonka; Romain Lucchesi; C. Lardo; P. North; M. J. Irwin; G. Battaglia; V. Hill; Eline Tolstoy; Kim A. Venn; A. Helmi; A. Kaufer; F. Primas; Matthew Shetrone
Springer Link (Chiba Institute of Technology) · DOI
We present our analysis of the FLAMES dataset targeting the central 25′ region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team. Our sample is composed of red giant branch stars down to V ∼ 20.5 mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H] = −3.2 to −1.5 dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in [α/Fe] at ∼0.4 dex followed by a decrease above [Fe/H] ∼ −2 dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H] ∼ −2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.
Vasily Belokurov; Zephyr Penoyre; Semyeong Oh; Giuliano Iorio; S. T. Hodgkin; N. W. Evans; Andrew Everall; S. E. Koposov; Christopher A. Tout; R. G. Izzard; C. J. Clarke; A. G. A. Brown
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT For stars with unresolved companions, motions of the centre of light and that of mass decouple, causing a single-source astrometric model to perform poorly. We show that such stars can be easily detected with the reduced χ2 statistic, or renormalized unit weight error (RUWE), provided as part of Gaia DR2. We convert RUWE into the amplitude of the image centroid wobble, which, if scaled by the source distance, is proportional to the physical separation between companions (for periods up to several years). We test this idea on a sample of known spectroscopic binaries and demonstrate that the amplitude of the centroid perturbation scales with the binary period and the mass ratio as expected. We apply this technique to the Gaia DR2 data and show how the binary fraction evolves across the Hertzsprung–Russell diagram. The observed incidence of unresolved companions is high for massive young stars and drops steadily with stellar mass, reaching its lowest levels for white dwarfs. We highlight the elevated binary fraction for the nearby blue stragglers and blue horizontal branch stars. We also illustrate how unresolved hierarchical triples inflate the relative velocity signal in wide binaries. Finally, we point out a hint of evidence for the existence of additional companions to the hosts of extrasolar hot Jupiters.
L. Rimoldini; B. Holl; M. Audard; N. Mowlavï; K. Nienartowicz; D. W. Evans; L. P. Guy; I. Lecoeur-Taïbi; G. Jevardat De Fombelle; O. Marchal; M. Roelens; J. De Ridder; L. M. Sarro; S. Regibo; M. López; G. Clementini; V. Ripepi; R. Molinaro; A. Garofalo; L. Molnár; E. Plachy; Á. Juhász; L. Szabados; T. Lebzelter; D. Teyssier; L. Eyer
Astronomy and Astrophysics · DOI
Context. More than half a million of the 1.69 billion sources in Gaia Data Release 2 (DR2) are published with photometric time series that exhibit light variations during the 22 months of observation. Aims. An all-sky classification of common high-amplitude pulsators (Cepheids, long-period variables, δ Scuti/SX Phoenicis, and RR Lyrae stars) is provided for stars with brightness variations greater than 0.1 mag in G band. Methods. A semi-supervised classification approach was employed, firstly training multi-stage random forest classifiers with sources of known types in the literature, followed by a preliminary classification of the Gaia data and a second training phase that included a selection of the first classification results to improve the representation of some classes, before the improved classifiers were applied to the Gaia data. Dedicated validation classifiers were used to reduce the level of contamination in the published results. A relevant fraction of objects were not yet sufficiently sampled for reliable Fourier series decomposition, consequently classifiers were based on features derived from statistics of photometric time series in the G , G BP , and G RP bands, as well as from some astrometric parameters. Results. The published classification results include 195 780 RR Lyrae stars, 150 757 long-period variables, 8550 Cepheids, and 8882 δ Scuti/SX Phoenicis stars. All of these results represent candidates whose completeness and contamination are described as a function of variability type and classification reliability. Results are expressed in terms of class labels and classification scores, which are available in the vari_classifier_result table of the Gaia archive.
T. Wevers; Dheeraj R. Pasham; S van Velzen; G. Leloudas; S. Schulze; J. C. A. Miller‐Jones; P. G. Jonker; M. Gromadzki; E. Kankare; S. T. Hodgkin; Ł. Wyrzykowski; Z. Kostrzewa-Rutkowska; S. Moran; M. Berton; K. Maguire; F. Onori; S. Mattila; M. Nicholl
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) candidate AT 2018fyk/ASASSN–18ul discovered by ASAS–SN. The Swift light curve is atypical for a TDE, entering a plateau after ∼40 d of decline from peak. After 80 d the UV/optical light curve breaks again to decline further, while the X-ray emission becomes brighter and harder. In addition to broad H, He, and potentially O/Fe lines, narrow emission lines emerge in the optical spectra during the plateau phase. We identify both high-ionization (O iii) and low-ionization (Fe ii) lines, which are visible for ∼45 d. We similarly identify Fe ii lines in optical spectra of ASASSN–15oi 330 d after discovery, indicating that a class of Fe-rich TDEs exists. The spectral similarity between AT 2018fyk, narrow-line Seyfert 1 galaxies, and some extreme coronal line emitters suggests that TDEs are capable of creating similar physical conditions in the nuclei of galaxies. The Fe ii lines can be associated with the formation of a compact accretion disc, as the emergence of low-ionization emission lines requires optically thick, high-density gas. Taken together with the plateau in X-ray and UV/optical luminosity this indicates that emission from the central source is efficiently reprocessed into UV/optical wavelengths. Such a two-component light curve is very similar to that seen in the TDE candidate ASASSN–15lh, and is a natural consequence of a relativistic orbital pericentre.
L. Eyer; L. Rimoldini; L. Rohrbasser; B. Holl; M. Audard; Dafydd Wyn Evans; Pedro García-Lario; P. Gavras; G. Clementini; S. T. Hodgkin; G. Jévardat de Fombelle; Alessandro C. Lanzafame; T. Lebzelter; Lecoeur-Taibi, I.; N. Mowlavï; K. Nienartowicz; V. Ripepi; Ł. Wyrzykowski
arXiv (Cornell University) · DOI
Stellar variability studies are now reaching a completely new level thanks to ESA's Gaia mission, which enables us to locate many variable stars in the Hertzsprung-Russell diagram and determine the various instability strips/bands. Furthermore, this mission also allows us to detect, characterise and classify many millions of new variable stars thanks to its very unique nearly simultaneous multi-epoch survey with different instruments (photometer, spectro-photometer, radial velocity spectrometer). An overview of what can be found in literature in terms of mostly data products by the Gaia consortium is given. This concerns the various catalogues of variable stars derived from the Gaia time series and also the location and motion of variable stars in the observational Hertzsprung-Russell diagram. In addition, we provide a list of a few thousands of variable white dwarf candidates derived from the DR2 published data, among them probably many hundreds of new pulsating white dwarfs. On a very different topic, we also show how Gaia allows us to reveal the 3D structures of and around the Milky Way thanks to the RR Lyrae stars.
R. Shirley; Y. Roehlly; Peter D. Hurley; V. Buat; María del Carmen Campos Varillas; Steven Duivenvoorden; K. J. Duncan; A. Efstathiou; D. Farrah; E. González-Solares; K. Małek; L. Marchetti; I. McCheyne; Andreas Papadopoulos; Estelle Pons; Roberto Scipioni; M. Vaccari; Seb Oliver
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT We present an optical to near-infrared (NIR) selected astronomical catalogue covering 1270 deg2. This is the first attempt to systematically combine data from 23 of the premier extragalactic survey fields – the product of a vast investment of telescope time. The fields are those imaged by the Herschel Space Observatory that form the Herschel Extragalactic Legacy Project (HELP). Our catalogue of 170 million objects is constructed by a positional cross-match of 51 public surveys. This high-resolution optical, NIR, and mid-infrared catalogue is designed for photometric redshift estimation, extraction of fluxes in lower resolution far-infrared maps, and spectral energy distribution modelling. It collates, standardizes, and provides value added derived quantities including corrected aperture magnitudes and astrometry correction over the Herschel extragalactic wide fields for the first time. $grizy$ fluxes are available on all fields with g-band data reaching $5\sigma$ point-source depths in a 2 arcsec aperture of 23.5, 24.4, and 24.6 (AB) mag at the 25th, 50th, and 75th percentiles, by area covered, across all HELP fields. It has K or $K_s$ coverage over 1146 deg2 with depth percentiles of 20.2, 20.4, and 21.0 mag, respectively. The IRAC Ch 1 band is available over 273 deg2 with depth percentiles of 17.7, 21.4, and 22.2 mag, respectively. This paper defines the ‘masterlist’ objects for the first data release (DR1) of HELP. This large sample of standardized total and corrected aperture fluxes, uniform quality flags, and completeness measures provides large well-understood statistical samples over the full Herschel extragalactic sky.
G. Marton; P. Ábrahám; E. Szegedi-Elek; J. Varga; M. Kun; Á. Kóspál; E. Varga-Verebélyi; S. T. Hodgkin; L. Szabados; Robert E. Beck; Csaba Kiss
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT The second Gaia Data Release (DR2) contains astrometric and photometric data for more than 1.6 billion objects with mean Gaia G magnitude &amp;lt;20.7, including many Young Stellar Objects (YSOs) in different evolutionary stages. In order to explore the YSO population of the Milky Way, we combined the Gaia DR2 data base with Wide-field Infrared Survey Explorer (WISE) and Planck measurements and made an all-sky probabilistic catalogue of YSOs using machine learning techniques, such as Support Vector Machines, Random Forests, or Neural Networks. Our input catalogue contains 103 million objects from the DR2xAllWISE cross-match table. We classified each object into four main classes: YSOs, extragalactic objects, main-sequence stars, and evolved stars. At a 90 per cent probability threshold, we identified 1 129 295 YSO candidates. To demonstrate the quality and potential of our YSO catalogue, here we present two applications of it. (1) We explore the 3D structure of the Orion A star-forming complex and show that the spatial distribution of the YSOs classified by our procedure is in agreement with recent results from the literature. (2) We use our catalogue to classify published Gaia Science Alerts. As Gaia measures the sources at multiple epochs, it can efficiently discover transient events, including sudden brightness changes of YSOs caused by dynamic processes of their circumstellar disc. However, in many cases the physical nature of the published alert sources are not known. A cross-check with our new catalogue shows that about 30 per cent more of the published Gaia alerts can most likely be attributed to YSO activity. The catalogue can be also useful to identify YSOs among future Gaia alerts.
Laura Hermosa Muñoz; Salvatore Taibi; G. Battaglia; Giuliano Iorio; M. Rejkuba; Ryan Leaman; Andrew A. Cole; M. J. Irwin; P. Jablonka; N. Kacharov; Alan W. McConnachie; Else Starkenburg; Eline Tolstoy
Astronomy and Astrophysics · DOI
Context. Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to have interacted with the large LG spirals, and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution. Aims. We provide insight into the internal mechanisms shaping LG dwarf galaxies by increasing our knowledge of the internal properties of isolated systems. Here we focus on the evolved stellar component of the Aquarius dwarf galaxy, whose kinematic and metallicity properties have only recently started to be explored. Methods. Spectroscopic data in the region of the near-infrared Ca II triplet lines has been obtained with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars. These data are used to derive line-of-sight (l.o.s.) velocities and [Fe/H] of the individual RGB stars. Results. We derive a systemic velocity of −142.2 +1.8 −1.8 km s −1 , in agreement with previous determinations from both the HI gas and stars. The internal kinematics of Aquarius appears to be best modelled by a combination of random motions (l.o.s. velocity dispersion of 10.3 +1.6 −1.3 km s −1 ) and linear rotation (with a gradient −5.0 +1.6 −1.9 km s −1 arcmin −1 ) along a PA = 139 +17 −27 deg, broadly consistent with the optical projected major axis. This rotation signal is significantly misaligned or even counter-rotating to that derived from the HI gas. We also find the tentative presence of a mild negative metallicity gradient and indications that the metal-rich stars have a colder velocity dispersion than the metal-poor ones. Conclusions. This work represents a significant improvement with respect to previous measurements of the RGB stars of Aquarius as it doubles the number of member stars already studied in the literature. We speculate that the misaligned rotation between the HI gas and evolved stellar component might have been the result of recent accretion of HI gas, or re-accretion after gas-loss due to internal stellar feedback.