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641. LAMOST DR4 New mercury-manganese stars
ID:
ivo://CDS.VizieR/J/A+A/645/A34
Title:
LAMOST DR4 New mercury-manganese stars
Short Name:
J/A+A/645/A34
Date:
21 Oct 2021
Publisher:
CDS
Description:
The present work presents our efforts at identifying new mercury-manganese (HgMn/CP3) stars using spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Suitable candidates were searched for among pre-selected early-type spectra from LAMOST DR4 using a modified version of the MKCLASS code that probes several HgII and MnII features. The spectra of the resulting 332 candidates were visually inspected. Using parallax data and photometry from Gaia DR2, we investigated magnitudes, distances from the Sun, and the evolutionary status of our sample stars. We also searched for variable stars using diverse photometric survey sources. We present 99 bona fide CP3 stars, 19 good CP3 star candidates, and seven candidates. Our sample consists of mostly new discoveries and contains, on average, the faintest CP3 stars known (peak distribution 9.5<=G<=13.5mag). All stars are contained within the narrow spectral temperature-type range from B6 to B9.5, in excellent agreement with the expectations and the derived mass estimates (2.4<=M_{sun}_<=4 for most objects). Our sample stars are between 100Myr and 500Myr old and cover the whole age range from zero-age to terminal-age main sequence. They are almost homogeneously distributed at fractional ages on the main sequence <=80%, with an apparent accumulation of objects between fractional ages of 50% to 80%. We find a significant impact of binarity on the mass and age estimates. Eight photometric variables were discovered, most of which show monoperiodic variability in agreement with rotational modulation. Together with the recently published catalogue of APOGEE CP3 stars, our work significantly increases the sample size of known Galactic CP3 stars, paving the way for future in-depth statistical studies.
642. LAMOST spectroscopic binaries & variable stars
ID:
ivo://CDS.VizieR/J/other/RAA/19.64
Title:
LAMOST spectroscopic binaries & variable stars
Short Name:
J/other/RAA/19.6
Date:
21 Oct 2021
Publisher:
CDS
Description:
About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than 10km/s and they are possible spectroscopic binary or variable candidates (SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760K and 4870K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621cm/s^2^. The locations of SBVCs on the [Fe/H]-T, [Fe/H]-logg, logg-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher logg~4.621 and lower T~4870K which are mainly cool red dwarf binaries. The second group of SBVCs has logg around 4.171cm/s^2^ that includes binaries and pulsating stars such as {delta} Sct and {gamma} Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary stage. The last group is composed of giants or supergiants with logg around 2.461cm/s^2^ that may be evolved pulsating stars. One target (C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65-days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.
643. Large-amplitude variables in Gaia DR2
ID:
ivo://CDS.VizieR/J/A+A/648/A44
Title:
Large-amplitude variables in Gaia DR2
Short Name:
J/A+A/648/A44
Date:
21 Oct 2021
Publisher:
CDS
Description:
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 twenty. The second data release (DR2) of the mission provides mean G, GBP and GRP 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 0.2mag in the G band for objects with mean brightnesses between 5.5 and 19mag. To achieve this, we rely on variability amplitude proxies in G, GBP and GRP computed from the uncertainties on the magnitudes published in DR2. We then apply successive filters to identify two subsets containing respectively sources with reliable mean GBP and GRP (for studies using colours) and sources having compatible amplitude proxies in G, GBP and GRP (for multi-band variability studies). The full catalogue gathers 23315874 LAV candidates, and the two subsets with increased levels of purity contain respectively 1148861 and 618966 sources. A multi-band variability analysis of the catalogue shows that different types of variable stars can be categorized according to their colour and blue-to-red amplitude ratios as determined from the G, GBP and GRP amplitude proxies. More specifically, four groups are globally identified. They mostly 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 with still 10% of them having 20% to 50% larger amplitudes in the blue than in the red. The catalogue constitutes the first census of Gaia large amplitude variable (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.
644. Large-amplitude variables near the Galactic Centre
ID:
ivo://CDS.VizieR/J/MNRAS/321/77
Title:
Large-amplitude variables near the Galactic Centre
Short Name:
J/MNRAS/321/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report here the results of a 4-yr K-band (2.2mm) survey for large-amplitude variable stars in a 24x24arcmin^2^ area centred on the Galactic Centre. A total of 409 likely long-period variables (LPVs) were detected, for which positions, amplitudes, average magnitudes and periods were obtained whenever possible. The surface density of LPVs is more than ten times greater than in the Sgr I Baade window at l=-1.37{deg}, b=-2.63{deg}
645. l Car radial velocity curves
ID:
ivo://CDS.VizieR/J/MNRAS/463/1707
Title:
l Car radial velocity curves
Short Name:
J/MNRAS/463/1707
Date:
21 Oct 2021
Publisher:
CDS
Description:
This work reports the discovery of cycle-to-cycle modulated spectral line and atmospheric velocity gradient variability in long-period Cepheids based on 925 high-resolution optical spectra of l Carinae (P~35.5d) recorded during three heavy duty-cycle monitoring campaigns (in 2014, 2015, and 2016). Spectral line variability is investigated via cross-correlation functions (CCFs) computed using three sets of spectral lines (weak, solar, strong). A metallic line velocity gradient, {delta}v_r_(t), is computed as the difference between weak and strong-line RVs. CCF shape indicators BIS (asymmetry), FWHM, and depth all exhibit clear phase-dependent variability patterns that differ from one pulsation cycle to the next. Weak-line CCFs exhibit these effects more clearly than strong-line CCFs. BIS exhibits the most peculiar modulated variability and can be used to identify the presence of cycle-to-cycle modulated line profile variations. {delta}v_r_(t) clearly exhibits cycle-to-cycle differences that correlate very closely with modulated BIS variability, suggesting perturbations of the atmospheric velocity field as the cause for modulated spectral line variability. These perturbations are most significant during contraction and are not in phase with the pulsation, transmitting information between consecutive pulsation cycles. This work shows RV curve modulation to be a consequence of atmospheric velocity gradient perturbations. Possible origins of these perturbations and their impact on Cepheid RV measurements as well as the projection factor used in Baade-Wesselink-type distance determinations are discussed.
646. LCID project. I. Cetus and Tucana variables
ID:
ivo://CDS.VizieR/J/ApJ/699/1742
Title:
LCID project. I. Cetus and Tucana variables
Short Name:
J/ApJ/699/1742
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first study of the variable star populations in the isolated dwarf spheroidal galaxies (dSphs) Cetus and Tucana. Based on Hubble Space Telescope images obtained with the Advanced Camera for Surveys in the F475W and F814W bands, we identified 180 and 371 variables in Cetus and Tucana, respectively. The vast majority are RR Lyrae stars. In Cetus, we also found three anomalous Cepheids (ACs), four candidate binaries and one candidate long-period variable (LPV), while six ACs and seven LPV candidates were found in Tucana. Of the RR Lyrae stars, 147 were identified as fundamental mode (RRab) and only eight as first-overtone mode (RRc) in Cetus, with mean periods of 0.614 and 0.363 day, respectively. In Tucana, we found 216 RRab and 82 RRc giving mean periods of 0.604 and 0.353 day. These values place both galaxies in the so-called Oosterhoff Gap, as is generally the case for dSph. We found numerous RR Lyrae variables pulsating in both modes simultaneously (RRd): 17 in Cetus and 60 in Tucana. We provide the photometry and pulsation parameters for all the variables, and compare the latter with values from the literature for well studied dSph of the Local Group and Galactic globular clusters. The parallel WFPC2 fields were also searched for variables, as they lie well within the tidal radius of Cetus, and at its limit in the case of Tucana. No variables were found in the latter, while 15 were discovered in the outer field of Cetus (11 RRab, three RRc, and one RRd), even though the lower signal-to-noise ratio of the observations did not allow us to measure their periods accurately. We provide their coordinates and approximate properties for completeness.
647. LCID project. II. Variables in IC1613
ID:
ivo://CDS.VizieR/J/ApJ/712/1259
Title:
LCID project. II. Variables in IC1613
Short Name:
J/ApJ/712/1259
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a new search for variable stars in the Local Group (LG) isolated dwarf galaxy IC 1613, based on 24 orbits of F475W and F814W photometry from the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. We detected 259 candidate variables in this field, of which only 13 (all of them bright Cepheids) were previously known. Out of the confirmed variables, we found 90 RR Lyrae stars, 49 classical Cepheids (including 36 new discoveries), and 38 eclipsing binary stars for which we could determine a period. The RR Lyrae include 61 fundamental (RRab) and 24 first-overtone (FO, RRc) pulsators, and five pulsating in both modes simultaneously (RRd). As for the majority of LG dwarfs, the mean periods of the RRab and RRc (0.611 and 0.334 days, respectively) as well as the fraction of overtone pulsators (f_c_=0.28) place this galaxy in the intermediate regime between the Oosterhoff types. From their position on the period-luminosity diagram and light-curve morphology, we can unambiguously classify 25 and 14 Cepheids as fundamental and FO mode pulsators, respectively. Another two are clearly second-overtone Cepheids, the first ones to be discovered beyond the Magellanic Clouds. Among the remaining candidate variables, five were classified as {delta}-Scuti and five as long-period variables. Most of the others are located on the main sequence, the majority of them likely eclipsing binary systems, although some present variations similar to pulsating stars.
648. LCID project VIII. Cepheids of Leo A
ID:
ivo://CDS.VizieR/J/MNRAS/432/3047
Title:
LCID project VIII. Cepheids of Leo A
Short Name:
J/MNRAS/432/3047
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a new search for variable stars in the Local Group dwarf galaxy Leo A, based on deep photometry from the Advanced Camera for Surveys onboard the Hubble Space Telescope. We detected 166 bona fide variables in our field, of which about 60% are new discoveries and 33 candidate variables. Of the confirmed variables, we found 156 Cepheids, but only 10 RR Lyrae stars despite nearly 100percent completeness at the magnitude of the horizontal branch. The RR Lyrae stars include seven fundamental and three first-overtone pulsators, with mean periods of 0.636 and 0.366d, respectively. From their position on the period-luminosity (PL) diagram and light-curve morphology, we classify 91, 58 and 4 Cepheids as fundamental, first-overtone and second-overtone mode Classical Cepheids (CC), respectively, and two as Population II Cepheids. However, due to the low metallicity of Leo A, about 90percent of the detected Cepheids have periods shorter than 1.5d. Comparison with theoretical models indicate that some of the fainter stars classified as CC could be Anomalous Cepheids. We estimate the distance to Leo A using the tip of the red giant branch (TRGB) and various methods based on the photometric and pulsational properties of the Cepheids and RR Lyrae stars. The distances obtained with the TRGB and RR Lyrae stars agree well with each other while that from the Cepheid PL relations is somewhat larger, which may indicate a mild metallicity effect on the luminosity of the short-period Cepheids. Due to its very low metallicity, Leo A thus serves as a valuable calibrator of the metallicity dependences of the variable star luminosities.
649. LCs of the RR Lyrae stars V350 Lyr & KIC 7021124
ID:
ivo://CDS.VizieR/J/ApJ/809/L19
Title:
LCs of the RR Lyrae stars V350 Lyr & KIC 7021124
Short Name:
J/ApJ/809/L19
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recent photometric space missions, such as CoRoT and Kepler, revealed that many RR Lyrae stars pulsate --beyond their main radial pulsation mode-- in low-amplitude modes. Space data seem to indicate a clear trend that, namely, overtone (RRc) stars and modulated fundamental (RRab) RR Lyrae stars ubiquitously show additional modes, while non-Blazhko RRab stars never do. Two Kepler stars (V350Lyr and KIC7021124), however, apparently seemed to break this rule: they were classified as non-Blazhko RRab stars showing additional modes. We processed Kepler pixel photometric data of these stars. We detected a small amplitude (but significant) Blazhko effect for both stars by using the resulting light curves and O-C diagrams. This finding strengthens the apparent connection between the Blazhko effect and the excitation of additional modes. In addition, it yields a potential tool for detecting Blazhko stars through the additional frequency patterns, even if we have only short but accurate time series observations. V350 Lyr shows the smallest amplitude multiperiodic Blazhko effect ever detected.
650. LCs re-analysis of Mira variables in ASAS
ID:
ivo://CDS.VizieR/J/ApJS/227/6
Title:
LCs re-analysis of Mira variables in ASAS
Short Name:
J/ApJS/227/6
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have developed an interactive PYTHON code and derived crucial ephemeris data of 99.4% of all stars classified as "Mira" in the ASAS database, referring to pulsation periods, mean maximum magnitudes, and whenever possible, the amplitudes among others. We present a statistical comparison between our results and those given by the International Variable Star Index (VSX) of the American Association of Variable Star Observers, as well as those determined with the machine learning automatic procedure of Richards et al. (2012, J/ApJS/203/32). Our periods are in good agreement with those of the VSX in more than 95% of the stars. However, when comparing our periods with those of Richards et al., the coincidence rate is only 76% and most of the remaining cases refer to aliases. We conclude that automatic codes still require more refinements in order to provide reliable period values. Period distributions of the target stars show three local maxima around 215, 275, and 330 days, apparently of universal validity; their relative strength seems to depend on galactic longitude. Our visual amplitude distribution turns out to be bimodal, however, 1/3 of the targets have rather small amplitudes (A<2.5^m^) and could refer to semiregular variables (SR). We estimate that about 20% of our targets belong to the SR class. We also provide a list of 63 candidates for period variations and a sample of 35 multiperiodic stars that seem to confirm the universal validity of typical sequences in the double period and in the Petersen diagrams.