Stellar mass and age determinations Mowlavi, N.; Eggenberger, P.; Meynet, G. ...
Astronomy and astrophysics (Berlin),
5/2012, Letnik:
541
Journal Article
We present the analysis of a 100 ks INTEGRAL (3-100 ${\rm keV}$) observation of the transient X-ray pulsar V 0332${+}53$in outburst. The source is pulsating at $P_{\rm Pulse}=4.3751\pm0.0002$ s with ...a clear double pulse from 6 ${\rm keV}$to 60 ${\rm keV}$. The average flux was ~550 mCrab between 20 ${\rm keV}$and 60 ${\rm keV}$. We modeled the broad band continuum from 5 ${\rm keV}$to 100 ${\rm keV}$with a power-law modified by an exponential cut off. We observe three cyclotron lines: the fundamental line at 24.9${^{+0.1}_{-0.1}}$ ${\rm keV}$, the first harmonic at 50.5${^{+0.1}_{-0.1}}$ ${\rm keV}$as well as the second harmonic at 71.7${^{+0.7}_{-0.8}}$ ${\rm keV}$, thus confirming the discovery of the harmonic lines by Coburn et al. (2005) in RXTEdata.
Context.
The intermediate-mass pre-main sequence Herbig Ae/Be stars are key to understanding the differences in formation mechanisms between low- and high-mass stars. The study of the general ...properties of these objects is hampered by the lack of a well-defined, homogeneous sample, and because few and mostly serendipitously discovered sources are known.
Aims.
Our goal is to identify new Herbig Ae/Be candidates to create a homogeneous and well defined catalogue of these objects.
Methods.
We have applied machine learning techniques to 4 150 983 sources with data from
Gaia
DR2, 2MASS, WISE, and IPHAS or VPHAS+. Several observables were chosen to identify new Herbig Ae/Be candidates based on our current knowledge of this class, which is characterised by infrared excesses, photometric variabilities, and H
α
emission lines. Classical techniques are not efficient for identifying new Herbig Ae/Be stars mainly because of their similarity with classical Be stars, with which they share many characteristics. By focusing on disentangling these two types of objects, our algorithm has also identified new classical Be stars.
Results.
We have obtained a large catalogue of 8470 new pre-main sequence candidates and another catalogue of 693 new classical Be candidates with a completeness of 78.8 ± 1.4% and 85.5 ± 1.2%, respectively. Of the catalogue of pre-main sequence candidates, at least 1361 sources are potentially new Herbig Ae/Be candidates according to their position in the Hertzsprung-Russell diagram. In this study we present the methodology used, evaluate the quality of the catalogues, and perform an analysis of their flaws and biases. For this assessment, we make use of observables that have not been accounted for by the algorithm and hence are selection-independent, such as coordinates and parallax based distances. The catalogue of new Herbig Ae/Be stars that we present here increases the number of known objects of the class by an order of magnitude.
Gaia Data Release 3 Lebzelter, T.; Mowlavi, N.; Lecoeur-Taibi, I. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Odprti dostop
Context.
The third
Gaia
Data Release covers 34 months of data and includes the second
Gaia
catalogue of long-period variables (LPVs), with
G
variability amplitudes larger than 0.1 mag (5–95% quantile ...range).
Aims.
The paper describes the production and content of the second
Gaia
catalogue of LPVs and the methods we used to compute the published variability parameters and identify C-star candidates.
Methods.
We applied various filtering criteria to minimise contamination from variable star types other than LPVs. The period and amplitude of the detected variability were derived from model fits to the
G
-band light curve wherever possible. C stars were identified using their molecular signature in the low-resolution RP spectra.
Results.
The catalogue contains 1 720 558 LPV candidates, including 392 240 stars with published periods (ranging from 35 to ∼1000 days) and 546 468 stars classified as C-star candidates. Comparison with literature data (OGLE and ASAS-SN) leads to an estimated completeness of 80%. The recovery rate is about 90% for the most regular stars (typically miras) and 60% for SRVs and irregular stars. At the same time, the number of known LPVs is increased by a factor of 6 with respect to literature data for amplitudes larger than 0.1 mag in
G
, and the contamination is estimated to be below 2%. Our C-star classification, based on solid theoretical arguments, is consistent with spectroscopically identified C stars in the literature. Caution must be taken in crowded regions, however, where the signal-ro-noise ratio of the RP spectra can become very low, or if the source is reddened by some kind of extinction. The quality and potential of the catalogue are illustrated by presenting and discussing LPVs in the solar neighbourhood, in globular clusters, and in galaxies of the Local Group.
Conclusions.
This is the largest all-sky LPVs catalogue to date. The photometric depth reaches
G
= 20 mag. This is a unique dataset for research into the late stages of stellar evolution.
Gaia Data Release 2 Mowlavi, N.; Lecoeur-Taïbi, I.; Lebzelter, T. ...
Astronomy and astrophysics (Berlin),
10/2018, Letnik:
618
Journal Article
Recenzirano
Odprti dostop
Context. Gaia
Data Release 2 (DR2) provides a unique all-sky catalogue of 550 737 variable stars, of which 151 761 are long-period variable (LPV) candidates with
G
variability amplitudes larger than ...0.2 mag (5–95% quantile range). About one-fifth of the LPV candidates are Mira candidates, the majority of the rest are semi-regular variable candidates. For each source,
G
,
G
BP
, and
G
RP
photometric time-series are published, together with some LPV-specific attributes for the subset of 89 617 candidates with periods in
G
longer than 60 days.
Aims.
We describe this first
Gaia
catalogue of LPV candidates, give an overview of its content, and present various validation checks.
Methods.
Various samples of LPVs were used to validate the catalogue: a sample of well-studied very bright LPVs with light curves from the American Association of Variable Star Observers that are partly contemporaneous with
Gaia
light curves, a sample of
Gaia
LPV candidates with good parallaxes, the All-Sky Automated Survey for Supernovae catalogue of LPVs, and the Optical Gravitational Lensing Experiment (OGLE) catalogues of LPVs towards the Magellanic Clouds and the Galactic bulge.
Results.
The analyses of these samples show a good agreement between
Gaia
DR2 and literature periods. The same is globally true for bolometric corrections of M-type stars. The main contaminant of our DR2 catalogue comes from young stellar objects (YSOs) in the solar vicinity (within ~1 kpc), although their number in the whole catalogue is only at the percent level. A cautionary note is provided about parallax-dependent LPV attributes published in the catalogue.
Conclusions.
This first
Gaia
catalogue of LPVs approximately doubles the number of known LPVs with amplitudes larger than 0.2 mag, despite the conservative candidate selection criteria that prioritise low contamination over high completeness, and despite the limited DR2 time coverage compared to the long periods characteristic of LPVs. It also contains a small set of YSO candidates, which offers the serendipitous opportunity to study these objects at an early stage of the
Gaia
data releases.
Context.
The period-luminosity diagram (PLD) has proven to be a powerful tool for studying populations of pulsating red giants.
Gaia
Data Release 2 (DR2) provides a large data set including many ...long-period variables (LPVs) on which this tool can be applied.
Aims.
We investigate the location of LPVs from the Large and Small Magellanic Clouds in the PLD using various optical and infrared luminosity indicators from
Gaia
and 2MASS, respectively. We thereby distinguish between stars of different masses and surface chemistry.
Methods.
The data set taken from the
Gaia
DR2 catalogue of LPVs allows for a homogeneous study from low- to high-mass LPVs. These sources are divided into sub-populations of asymptotic giant branch (AGB) stars according to their mass and their O- or C-rich nature using the
Gaia
-2MASS diagram developed by our group. This diagram uses a Wesenheit index
W
BP, RP
based on Wesenheit functions in the
Gaia
and 2MASS photometric bands. Four different luminosity indicators are used to study the period-luminosity (P–L) relations.
Results.
We provide the first observational evidence of a P–L relation offset for both fundamental and 1O pulsators between low- and intermediate-mass O-rich stars, in agreement with published pulsation predictions. Among the luminosity indicators explored, sequence C′ is the narrowest in the
P
–
W
BP, RP
diagram, and is thus to be preferred over the other PLDs for the determination of distances using LPVs. The majority of massive AGB stars and red supergiants form a smooth extension of sequence C of low- and intermediate-mass AGB stars in the
P
–
W
BP, RP
diagram, suggesting that they pulsate in the fundamental mode. All results are similar in the two Magellanic Clouds.
Gaia Data Release 3 Gomel, R.; Mazeh, T.; Faigler, S. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Odprti dostop
As part of
Gaia
Data Release 3, a large number of ellipsoidal variables were identified with supervised classification. The periodic variability of these ellipsoidals is presumably induced by tidal ...interaction with a companion in a close binary system. We present 6306 short-period probable ellipsoidal variables with relatively large-amplitude
Gaia
G
-band photometric modulations that indicate a possible massive, undetected secondary. In case of a main-sequence primary, the more massive secondary is probably a compact object – either a black hole or a neutron star, and sometimes a white dwarf. The identification is based on the recently suggested robust modified minimum mass ratio (mMMR) that was derived from the observed ellipsoidal amplitude alone, without the use of the primary mass or radius. We also list a subset of 262 systems with an mMMR higher than unity, for which the probability of a compact secondary is higher. Follow-up observations are needed to verify the true nature of these variables.
Gaia Data Release 3 Clementini, G.; Ripepi, V.; Garofalo, A. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Odprti dostop
Context.
RR Lyrae stars are excellent tracers of the oldest stars (ages ≳ 9–10 Gyr) and standard candles for measuring the distance to stellar systems that are mainly composed of an old stellar ...population. The
Gaia
Third Data Release (DR3) publishes a catalogue of full-sky RR Lyrae stars observed during the initial 34 months of science operations. They were processed through the Specific Object Study (SOS) pipeline, which was developed to validate and characterise Cepheids and RR Lyrae stars (SOS Cep&RRL) observed by
Gaia
.
Aims.
The main steps of the SOS Cep&RRL pipeline are described in the documentation and papers accompanying previous
Gaia
data releases. For DR3, the pipeline was modified in its process: in addition to the
Gaia
multiband (
G
,
G
BP
,
G
RP
) time-series photometry, the epoch radial velocities measured for RR Lyrae and Cepheids with the Radial Velocity Spectrometer (RVS) on board
Gaia
were also processed through the pipeline.
Methods.
The SOS Cep&RRL validation of DR3 candidate RR Lyrae stars relies on diagnostics tools that include the period versus
G
-amplitude diagram and the period versus
ϕ
21
and
ϕ
31
parameters of the
G
light-curve Fourier decomposition, as defined by a reference sample of bona fide RR Lyrae stars known in the literature (that we named Gold Sample). Great care was devoted to building a large and pure Gold Sample comprising more than 200 000 RR Lyrae stars. The SOS processing led to an initial catalogue of 271779 RR Lyrae stars that are listed in the
vari_rrlyrae
table of the DR3 archive. A thorough cleaning procedure was then performed to produce a final catalogue of SOS-confirmed DR3 RR Lyrae stars by dropping sources that clearly are contaminants or have an uncertain classification.
Results.
Multiband time-series photometry and characterisation are published in
Gaia
DR3 for a clean, validated sample of 270 905 RR Lyrae stars (174 947 fundamental-mode, 93 952 first-overtone, and 2006 double-mode RR Lyrae) that were confirmed and fully characterised by the SOS Cep&RRL pipeline. They are distributed throughout the sky, including variables in 95 globular clusters and 25 Milky Way (MW) companions (the Magellanic Clouds, seven dwarf spheroidal galaxies, and 16 ultra-faint dwarf satellites of the MW). RVS time-series radial velocities are also published for 1096 RR Lyrae and 799 Cepheids of different types (classical, anomalous, and type II Cepheids). Of the 270 905 DR3 RR Lyrae stars, 200 294 are already known in the literature (Gold Sample) and 70 611 are new discoveries by
Gaia
, to the best of our knowledge. An estimate of the interstellar absorption is published for 142 660 fundamental-mode RR Lyrae stars from a relation based on the
G
-band amplitude, the (
G
−
G
RP
) colour and the pulsation period. Metallicities derived from the Fourier parameters of the light curves are also released for 133 559 RR Lyrae stars.
Conclusions.
The final
Gaia
DR3 catalogue of confirmed RR Lyrae stars almost doubles the DR2 RR Lyrae catalogue. An increase in statistical significance, a better characterisation of the RR Lyrae pulsational and astrophysical parameters, and the improved astrometry published with
Gaia
EDR3 make the SOS Cep&RRL DR3 sample the largest, most homogeneous, and parameter-richest catalogue of all-sky RR Lyrae stars published so far in the magnitude range from ⟨
G
⟩=7.64 mag (the magnitude of RR Lyr itsef, the class prototype) to ⟨
G
⟩=21.14 mag (the faintest RR Lyrae in the catalogue).
Gaia Data Release 3 Eyer, L.; Audard, M.; Holl, B. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Odprti dostop
Context.
Gaia
has been in operations since 2014, and two full data releases (DR) have been delivered so far: DR1 in 2016 and DR2 in 2018. The third
Gaia
data release expands from the early data ...release (EDR3) in 2020, which contained the five-parameter astrometric solution and mean photometry for 1.8 billion sources by providing 34 months of multi-epoch observations that allowed us to systematically probe, characterise, and classify variable celestial phenomena.
Aims.
We present a summary of the variability processing and analysis of the photometric and spectroscopic time series of 1.8 billion sources carried out for
Gaia
DR3.
Methods.
We used statistical and machine learning methods to characterise and classify the variable sources. Training sets were built from a global revision of major published variable star catalogues. For a subset of classes, specific detailed studies were conducted to confirm their class membership and to derive parameters that are adapted to the peculiarity of the considered class.
Results.
In total, 10.5 million objects are identified as variable in
Gaia
DR3 and have associated time series in
G
,
G
BP
, and
G
RP
and, in some cases, radial velocity time series. The DR3 variable sources subdivide into 9.5 million variable stars and 1 million active galactic nuclei or ‘quasars’. In addition, supervised classification identified 2.5 million galaxies thanks to spurious variability induced by the extent of these objects. The variability analysis output in the DR3 archive amounts to 17 tables, containing a total of 365 parameters. We publish 35 types and subtypes of variable objects. For 11 variable types, additional specific object parameters are published. Here, we provide an overview of the estimated completeness and contamination of most variability classes.
Conclusions.
Thanks to
Gaia
, we present the largest whole-sky variability analysis based on coherent photometric, astrometric, and spectroscopic data. Future
Gaia
data releases will more than double the span of time series and the number of observations, allowing the publication of an even richer catalogue.
Context.
Photometric variability is an essential feature that sheds light on the intrinsic properties of celestial variable sources, the more so when photometry is available in various bands. In this ...respect, the all-sky
Gaia
mission is particularly attractive as it collects, among other quantities, epoch photometry measured quasi-simultaneously in three optical bands for sources ranging from a few magnitudes to fainter than magnitude 20.
Aims.
The second data release (DR2) of the mission provides mean
G
,
G
BP
, and
G
RP
photometry for ∼1.4 billion sources, but light curves and variability properties are available for only ∼0.5 million of them. Here, we provide a census of large-amplitude variables (LAVs) with amplitudes larger than ∼0.2 mag in the
G
band for objects with mean brightnesses between 5.5 and 19 mag.
Methods.
To achieve this, we rely on variability amplitude proxies in
G
,
G
BP
, and
G
RP
computed from the uncertainties on the magnitudes published in DR2. We then apply successive filters to identify two subsets containing sources with reliable mean
G
BP
and
G
RP
(for studies using colours) and sources having compatible amplitude proxies in
G
,
G
BP
, and
G
RP
(for multi-band variability studies).
Results.
The full catalogue gathers 23 315 874 LAV candidates, and the two subsets with increased levels of purity contain, respectively, 1 148 861 and 618 966 sources. A multi-band variability analysis of the catalogue shows that different types of variable stars can be categorized according to their colours and blue-to-red amplitude ratios as determined from the
G
,
G
BP
, and
G
RP
amplitude proxies. More specifically, four groups are globally identified. They include: long-period variables in a first group with amplitudes more than twice larger in the blue than in the red; hot compact variables in a second group with amplitudes smaller in the blue than in the red; classical instability strip pulsators in a third group with amplitudes larger in the blue than in the red by 50% to 80%; and other non-pulsating variables in a fourth group, mainly achromatic, but 10% of them still having 20% to 50% larger amplitudes in the blue than in the red.
Conclusions.
The catalogue constitutes the first census of
Gaia
LAV candidates extracted from the public DR2 archive. The overview presented here illustrates the added value of the mission for multi-band variability studies, even at this stage when epoch photometry is not yet available for all sources.
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