Search

Start Over Subject variable stars Capability Type Simple Cone Search
271. Fourier analysis of 13095 LMC RR Lyr stars
ID:
ivo://CDS.VizieR/J/MNRAS/438/2440
Title:
Fourier analysis of 13095 LMC RR Lyr stars
Short Name:
J/MNRAS/438/2440
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a careful and detailed light-curve analysis of publicly available I-band data on fundamental mode RR Lyrae (RRab) stars of the Large Magellanic Cloud (LMC) obtained by the Optical Gravitational Lensing Experiment phase-III project. Using the Fourier parameters of 13095 RRab stars, metallicities and absolute magnitudes of individual stars are obtained. The representation of stars on the P-{phi}_31_^V^ plane shows the existence of three significant metallicity groups with mean metallicities as -1.20+/-0.12, -1.57+/-0.10 and -1.89+/-0.09dex. The corresponding absolute magnitudes of these three groups are obtained as 0.70+/-0.08, 0.59+/-0.06 and 0.49+/-0.08mag, respectively. Distribution of these three groups as a function of vertical |z| distance indicates that the formation of the LMC disc predates the formation of the inner halo. Issue of the existence of a metallicity gradient as a function of galactocentric distances has also been addressed. Approximating the structure of the LMC disc as a triaxial ellipsoid, the inclination angle (i) relative to the plane of the sky and the position angle of the line of nodes ({theta}_lon_) were estimated as 24.20{deg} and 176.01{deg}, respectively. The axes ratios and the eccentricity were also determined using the principal axis transformation method.
272. Fourier parameters for Cepheid variables
ID:
ivo://CDS.VizieR/J/MNRAS/369/723
Title:
Fourier parameters for Cepheid variables
Short Name:
J/MNRAS/369/723
Date:
21 Oct 2021
Publisher:
CDS
Description:
The superb phase resolution and quality of the OGLE data on LMC and SMC Cepheids, together with existing data on Galactic Cepheids, are combined to study the period-colour (PC) and amplitude-colour (AC) relations as a function of pulsation phase. Our results confirm earlier work that the LMC PC relation (at mean light) is more consistent with two lines of differing slopes, separated at a period of 10 days. However, our multi-phase PC relations reveal much new structure which can potentially increase our understanding of Cepheid variables. These multi-phase PC relations provide insight into why the Galactic PC relation is linear but the LMC PC relation is non-linear. This is because the LMC PC relation is shallower for short (logP<1) and steeper for long (logP>1) period Cepheids than the corresponding Galactic PC relation. Both of the short and long period Cepheids in all three galaxies exhibit the steepest and shallowest slopes at phases around 0.75-0.85, respectively. A consequence is that the PC relation at phase ~0.8 is highly non-linear. Further, the Galactic and LMC Cepheids with logP>1 display a flat slope in the PC plane at phases close to the maximum light. When the LMC period- luminosity (PL) relation is studied as a function of phase, we confirm that it changes with the PC relation. The LMC PL relation in V- and I-band near the phase of 0.8 provides compelling evidence that this relation is also consistent with two lines of differing slopes joined at a period close to 10 days.
273. Frequency analysis of CoRoT B stars
ID:
ivo://CDS.VizieR/J/A+A/506/471
Title:
Frequency analysis of CoRoT B stars
Short Name:
J/A+A/506/471
Date:
21 Oct 2021
Publisher:
CDS
Description:
We search for new variable B-type pulsators in the CoRoT data assembled primarily for planet detection, as part of CoRoT's Additional Programme. We aim to explore the properties of newly discovered B-type pulsators from the uninterrupted CoRoT spacebased photometry and to compare them with those of known members of the beta Cep and slowly pulsating B star (SPB) classes. We developed automated data analysis tools which include algorithms for jump correction, light curve detrending, frequency detection, frequency combination search and frequency and period spacing search. Besides numerous new classical slowly pulsating B stars, we find evidence for a new class of low-amplitude B-type pulsators between the SPB and delta Sct instability strips, with a very broad range of frequencies and low amplitudes, as well as several slowly pulsating B stars with residual excess power at frequencies typically a factor three above their expected g-mode frequencies. The frequency data we obtained for numerous new B-type pulsators represent an appropriate starting point for further theoretical analyses of these stars, once their effective temperature, gravity, rotation velocity and abundances will be derived spectroscopically in the framework of an ongoing FLAMES survey at VLT.
274. Frequency analysis of fundamental-mode RR Lyrae
ID:
ivo://CDS.VizieR/J/ApJ/598/597
Title:
Frequency analysis of fundamental-mode RR Lyrae
Short Name:
J/ApJ/598/597
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have frequency-analyzed 6391 variables classified earlier as fundamental-mode RR Lyrae (RR0) stars in the MACHO database on the Large Magellanic Cloud (LMC). The overwhelming majority (i.e., 96%) of these variables have been proved to be indeed RR0 stars, whereas the remaining ones have fallen into one of the following categories: single- and double-mode Cepheids, binaries, first-overtone and double-mode RR Lyrae stars, and nonclassified variables. Special attention has been paid to the properties of the amplitude- and phase-modulated RR0 stars (the Blazhko stars). We found altogether 731 Blazhko variables showing either a doublet or an equidistant triplet pattern at the main pulsation component in their frequency spectra. This sample overwhelmingly exceeds the number of Blazhko stars known in all other systems combined. The incidence rate of the Blazhko variables among the RR0 stars in the LMC is 11.9%, which is 3 times higher than their rate among the first-overtone RR Lyrae stars. No difference is found in the average brightness between the single-mode and Blazhko variables. However, the latter ones show a somewhat lower degree of skewness in their average light curves and a concomitant lower total amplitude in their modulation-free light curves.
275. Frequency spacing of {delta} Scuti stars. II.
ID:
ivo://CDS.VizieR/J/ApJS/224/41
Title:
Frequency spacing of {delta} Scuti stars. II.
Short Name:
J/ApJS/224/41
Date:
21 Oct 2021
Publisher:
CDS
Description:
A sequence search method was developed for searching for regular frequency spacing in {delta} Scuti stars by visual inspection (VI) and algorithmic search. The sample contains 90 {delta} Scuti stars observed by CoRoT. An example is given to represent the VI. The algorithm (SSA) is described in detail in section 3.2. The data treatment of the CoRoT light curves, the criteria for frequency filtering, and the spacings derived by two methods (i.e., three approaches: VI, SSA, and FT (Fourier Transform)) are given for each target. Echelle diagrams are presented for 77 targets for which at least one sequence of regular spacing was identified. Comparing the spacing and the shifts between pairs of echelle ridges revealed that at least one pair of echelle ridges is shifted to midway between the spacing for 22 stars. The estimated rotational frequencies compared to the shifts revealed rotationally split doublets, triplets, and multiplets not only for single frequencies, but for the complete echelle ridges in 31 {delta} Scuti stars. Using several possible assumptions for the origin of the spacings, we derived the large separation ({Delta}_nu_) that are distributed along the mean density versus large separations relation derived from stellar models.
276. FU Ori multi-band interferometric observations
ID:
ivo://CDS.VizieR/J/A+A/646/A102
Title:
FU Ori multi-band interferometric observations
Short Name:
J/A+A/646/A102
Date:
21 Oct 2021
Publisher:
CDS
Description:
FU Orionis is the archetypal FUor star, a subclass of young stellar object (YSO) that undergo rapid brightening events, often gaining 4-6 magnitudes on timescales of days. This brightening is often associated with a massive increase in accretion; one of the most ubiquitous processes in astrophysics from planets and stars to super-massive black holes. We present multi-band interferometric observations of the FU Ori circumstellar environment, including the first J-band interferometric observations of a YSO. We investigate the morphology and temperature gradient of the inner-most regions of the accretion disk around FU Orionis. We aim to characterise the heating mechanisms of the disk and comment on potential outburst triggering processes. Methods. Recent upgrades to the MIRC-X instrument at the CHARA array allowed the first dual-band J and H observations of YSOs. Using baselines up to 331m, we present high angular resolution data of a YSO covering the near-infrared bands J, H, and K. The unprecedented spectral range of the data allows us to apply temperature gradient models to the innermost regions of FU Ori. We spatially resolve the innermost astronomical unit of the disk and determine the exponent of the temperature gradient of the inner disk to T{prop.to}r^-0.74+/-0.02^. This agrees with theoretical work that predicts T{prop.to}r^-0.75^ for actively accreting, steady state disks, a value only obtainable through viscous heating within the disk. We find a disk which extends down to the stellar surface at 0.015+/-0.007au where the temperature is found to be 5800+/-700K indicating boundary layer accretion. We find a disk inclined at 32+/-4{deg} with a minor-axis position angle of 34+/-11{deg}.
277. FUV-NUV observations of NGC 2808
ID:
ivo://CDS.VizieR/J/ApJ/625/156
Title:
FUV-NUV observations of NGC 2808
Short Name:
J/ApJ/625/156
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a reanalysis of far-ultraviolet (FUV) observations of the globular cluster NGC 2808 obtained with the Hubble Space Telescope. These data were first analyzed by Brown and coworkers (2001, Cat. <J/ApJ/562/368>), with an emphasis on the bright, blue horizontal-branch (HB) stars in this cluster. Here, our focus is on the population of fainter FUV sources, which include white dwarfs (WDs), blue stragglers (BSs), and cataclysmic variables (CVs).
278. Gaia Alerts with LAMOST and SDSS
ID:
ivo://CDS.VizieR/J/other/ApSS/365.89
Title:
Gaia Alerts with LAMOST and SDSS
Short Name:
J/other/ApSS/365
Date:
21 Oct 2021
Publisher:
CDS
Description:
The ESA-Gaia satellite is regularly producing Alerts on objects where photometric variability has been detected after several passages over the same region of the sky. The physical nature of these objects has often to be determined with the help of complementary observations from ground-based facilities. We have compared the list of Gaia Alerts (from the beginning in 2014 to Nov. 1st, 2018) with archival LAMOST and SDSS spectroscopic data. A search radius of 3" has been adopted. In using survey data, the date of the ground-based observation rarely corresponds to the date of the Alert, but this allows at least the identification of the source if it is persistent, or the host galaxy if the object was only transient like a supernova (SN). Some of the objects have several LAMOST observations, and we complemented this search by adding also SDSS DR15 data in order to look for long-term variability. A list of Gaia Nuclear Transients (GNT) from Kostrzewa-Rutkowska et al. (2018. 2018MNRAS.481..307K, Cat. J/MNRAS/481/307), has been included in this search also. We found 26 Gaia Alerts with spectra in LAMOST+SDSS labelled as stars, among which 12 have multi-epoch spectra. A majority of them are Cataclysmic Variables (CVs). Similarly, 206 Gaia Alerts have associated spectra labelled as galaxies, among which 49 have multi-epoch spectra. Those spectra were generally obtained on a date widely different from the Alert date, and are mostly emission-line galaxies with no particularity (except a few Seyferts), leading to the suspicion that most of the Alerts were due to a SN. As for the GNT list, we found 55 associated spectra labelled as galaxies, among them 13 with multi-epoch spectra. In these two galaxy samples, in only two cases, Gaia17aal and GNTJ170213+2543, was the date of the spectroscopic observation close enough to the Alert date: we find a trace of the SN itself in their LAMOST spectrum, both being now classified here as a type Ia SN. Compared to the galaxy sample from the Gaia alerts, the GNT sample has a higher proportion of AGNs, suggesting that some of the detected variations are also due to the AGN itself. Similarly for Quasars, we found only 30 Gaia Alerts but 68 GNT cases associated with single epoch quasar spectra in the databases. In addition to those, 12 plus 23 are quasars where multi-epoch spectra are available. For ten out of these 35, their multi-epoch spectra show appearance or disappearance of the broad Balmer lines and also variations in the continuum, qualifying them as "Changing Look Quasars" and therefore significantly increasing the available sample of such objects.
279. Gaia DR2
ID:
ivo://CDS.VizieR/I/345
Title:
Gaia DR2
Short Name:
I/345
Date:
21 Oct 2021
Publisher:
CDS
Description:
Gaia Data Release 2. Summary of the contents and survey properties: We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on as- trophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the G_BP_ (330-680nm) and G_RP_ (630-1050nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy. The catalogue of radial velocity standard stars (Soubiran et al., 2018A&A...616A...7S) The Radial Velocity Spectrometer (RVS) on board of Gaia having no calibration device, the zero point of radial velocities needs to be calibrated with stars proved to be stable at the level of 300m/s during the Gaia observations. A dataset of about 71000 ground-based radial velocity measurements from five high resolution spectrographs has been compiled. A catalogue of 4813 stars was built by combining these individual measurements. The zero point has been established using asteroids. The resulting catalogue has 7 observations per star on average on a typical time baseline of 6 years, with a median standard deviation of 15m/s. A subset of the most stable stars fulfilling the RVS requirements has been used to establish the zero point of the radial velocities provided in Gaia DR2. The stars not used for calibration are used for the RVS data validation.
280. Gaia DR1 and OGLE variable stars
ID:
ivo://CDS.VizieR/J/AcA/66/433
Title:
Gaia DR1 and OGLE variable stars
Short Name:
J/AcA/66/433
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comparison of the Gaia DR1 samples of pulsating variable stars - Cepheids and RR Lyr type - with the OGLE Collection of Variable Stars aiming at the characterization of the Gaia mission performance in the stellar variability domain. Out of 575 Cepheids and 2322 RR Lyr candidates from the Gaia DR1 samples located in the OGLE footprint in the sky, 559 Cepheids and 2302 RR Lyr stars are genuine pulsators of these types. The number of misclassified stars is low indicating reliable performance of the Gaia data pipeline. The completeness of the Gaia DR1 samples of Cepheids and RR Lyr stars is at the level of 60-75% as compared to the OGLE Collection dataset. This level of completeness is moderate and may limit the applicability of the Gaia data in many projects.