- ID:
- ivo://CDS.VizieR/J/A+AS/109/201
- Title:
- Variable stars in instability strip
- Short Name:
- J/A+AS/109/201
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Identifications, positions, photometry, spectra, some pulsational features, other astrophysical parameters and literature for 302 pulsating variable stars in the lower instability strip, near the ZAMS, are given. About 185 stars have near homogeneous photometric information in the Stroemgren's uvby-{beta} photometric system. This catalogue/database covers information published until November 1993.
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20492. Variable stars in Leo I dSph
- ID:
- ivo://CDS.VizieR/J/PASP/126/616
- Title:
- Variable stars in Leo I dSph
- Short Name:
- J/PASP/126/616
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From archival ground-based images of the Leo I dwarf spheroidal galaxy, we have identified and characterized the pulsation properties of 164 candidate RR Lyrae variables and 55 candidate anomalous and/or short-period Cepheids. We have also identified 19 candidate long-period variable stars and 13 other candidate variables whose physical nature is unclear, but due to the limitations of our observational material we are unable to estimate reliable periods for them.
- ID:
- ivo://CDS.VizieR/J/A+A/500/917
- Title:
- Variable stars in LMC MACHO fields 1 & 79
- Short Name:
- J/A+A/500/917
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because of the strong effect of systematics/trends in variable star observations, we apply the Trend Filtering Algorithm (TFA) to a subset of the MACHO database and search for variable stars. TFA has been applied successfully in planetary transit searches, where weak, short-lasting periodic dimmings are sought in the presence of noise and various systematics (due to, e.g., imperfect flat fielding, crowding, etc). These latter effects introduce colored noise in the photometric time series that can completely overwhelm the signal. By using a large number of available photometric time series of a given field, TFA utilizes the fact that the same types of systematics appear in several/many time series of the same field. As a result, we attempt to reproduce each target time series by a linear combination of templates, optimized by least-squares. After a signal has been identified in the residuals between the original time series and the systematics computed by TFA, we reconstruct the signal by employing the full model, including the signal, systematics and noise. We apply TFA to the brightest ~5300 objects from subsets of each of the MACHO Large Magellanic Cloud fields #1 and #79. We find that the Fourier frequency analysis performed on the original data detects some 60% of the objects as trend-dominated. This figure decreases essentially to zero after using TFA. In total, we detect 387 variables in the two fields, 183 of which would have remained undetected without using TFA. Where possible, we give preliminary classification of the variables found.
- ID:
- ivo://CDS.VizieR/J/ApJ/842/60
- Title:
- Variable stars in Logal Group galaxies. III.
- Short Name:
- J/ApJ/842/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of 1568 RR Lyrae stars in three of the most luminous M31 satellites: And VII (573), NGC 147 (177), and NGC 185 (818). We use their properties to study the formation history of Local Group spiral haloes, and in particular, to infer about the nature of their possible building blocks by comparison with available data for RR Lyrae stars in the halo and in a sample of satellites of M31 and the Milky Way. We find that the brightest satellites and the halos of both galaxies host a number of High Amplitude Short Period (HASP) RR Lyrae variable stars, which are missing in the faintest satellites. HASP variable stars have been shown by Fiorentino+ (2015ApJ...798L..12F) to be tracers of a population of stars as metal-rich as [Fe/H]~-1.5 and older than ~10Gyr. This suggests that the metal-rich M31 and MW halo component, which manifests through the HASP phenomenon, comes from massive dwarf galaxy building blocks, as the low-mass dwarfs did not chemically enrich fast enough to produce them. All detected variable stars are new discoveries; in particular, this work presents the first detections of RR Lyrae stars in And VII. Moreover, a number of candidate Anomalous Cepheids, and binary and long-period variable stars have been detected. We provide pulsation properties (period, amplitude, mean magnitude), light curves, and time series photometry for all of the variable stars in the three galaxies.
20495. Variable stars in M54
- ID:
- ivo://CDS.VizieR/J/MNRAS/406/329
- Title:
- Variable stars in M54
- Short Name:
- J/MNRAS/406/329
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new B, V and I CCD time-series photometry for 177 variable stars in a 13x13arcmin^2^ field centred on the globular cluster M54 using the European Southern Observatory (ESO)-Danish 1.54-m telescope in La Silla, 94 of which are newly identified variables. The total sample is composed of two anomalous Cepheids, 144 RR Lyrae stars (108 RR0 and 36 RR1), three SX Phoenicis, seven eclipsing binaries (five W UMa and two Algol binaries), three variables of uncertain classification and 18 long-period variables. Ephemerides are provided for all the observed short-period variables. The positional accuracy is better than 0.2".
20496. Variable stars in M92
- ID:
- ivo://CDS.VizieR/J/ApJ/87/361
- Title:
- Variable stars in M92
- Short Name:
- J/ApJ/87/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distance modulus of M92 is determined from the bright stars and the mean magnitude of 12 cluster-type variables. From the former, m-M=14.93; and from the latter, m-M=14.94+/-0.01. Two variables not belonging to the cluster are indicated, as well as two other stars with range in variation of 0.25mag, which are marked as probable variables. From star counts, the ratio of the minor to the major axis is found to be 0.85, with a position angle of the major axis of 28{deg}. Sensitometer tracings give 14' for the diameter of the cluster.
- ID:
- ivo://CDS.VizieR/J/ApJ/844/40
- Title:
- Variable stars in M31 and M33. V. HR diagram
- Short Name:
- J/ApJ/844/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present HR diagrams for the massive star populations in M31 and M33, including several different types of emission-line stars: the confirmed luminous blue variables (LBVs), candidate LBVs, B[e] supergiants, and the warm hypergiants. We estimate their apparent temperatures and luminosities for comparison with their respective massive star populations and evaluate the possible relationships of these different classes of evolved, massive stars, and their evolutionary state. Several of the LBV candidates lie near the LBV/S Dor instability strip that supports their classification. Most of the B[e] supergiants, however, are less luminous than the LBVs. Many are very dusty with the infrared flux contributing one-third or more to their total flux. They are also relatively isolated from other luminous OB stars. Overall, their spatial distribution suggests a more evolved state. Some may be post-RSGs (red supergiants) like the warm hypergiants, and there may be more than one path to becoming a B[e] star. There are sufficient differences in the spectra, luminosities, spatial distribution, and the presence or lack of dust between the LBVs and B[e] supergiants to conclude that one group does not evolve into the other.
- ID:
- ivo://CDS.VizieR/J/ApJ/449/164
- Title:
- Variable Stars in MC Clusters. II
- Short Name:
- J/ApJ/449/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study aimed at identifying variable stars in the rich LMC cluster NGC 1850. V and I band CCD imaging spanning more than 5 years in a 10'x10' field surrounding the cluster has allowed us to identify more than 30 variable stars, including seven classical Cepheids, one anomalous Cepheid, two RR Lyrae variables, 19 long-period variables (LPVs), one blue eclipsing binary, one possible pair of eclipsing giants, and several peculiar variables. The only likely cluster member is a Cepheid. Isochrone fitting to the cluster CMD yields an age of 80 Myr if an LMC distance modulus of 18.5 is adopted. A comparison of pulsation and evolution masses for the Cepheids still yields a ratio of evolution to pulsation mass of ~1.2 for evolution models computed with core overshoot parameter Lambda = 0.5, where Lambda = 2d_ov/H_p, d_ov is the distance that convection overshoots beyond the Schwarzschild boundary and H_p is the pressure scale height. An overshoot parameter Lambda ~ 1.0 would be required to bring the evolution and pulsation masses into agreement. One of the Cepheids in the field is a bump Cepheid. A calculation of the bump mass yields a value in reasonable agreement with the pulsation mass. We show that detailed modelling of individual bump Cepheids is capable of providing very tight constraints on the LMC distance modulus. The Cepheid period-luminosity-color relation compared to the theoretical relation yields a LMC distance modulus of 18.60. Finally, arguments are presented which suggest that the LPVs are a mixture of fundamental mode pulsators and small-amplitude overtone pulsators.
- ID:
- ivo://CDS.VizieR/J/ApJ/825/50
- Title:
- Variable stars in M31 & M33. III. YSGs & RSGs
- Short Name:
- J/ApJ/825/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent supernova (SN) and transient surveys have revealed an increasing number of non-terminal stellar eruptions. Though the progenitor class of these eruptions includes the most luminous stars, little is known of the pre-SN mechanics of massive stars in their most evolved state, thus motivating a census of possible progenitors. From surveys of evolved and unstable luminous star populations in nearby galaxies, we select a sample of yellow and red supergiant (RSG) candidates in M31 and M33 for review of their spectral characteristics and spectral energy distributions (SEDs). Since the position of intermediate- and late-type supergiants on the color-magnitude diagram can be heavily contaminated by foreground dwarfs, we employ spectral classification and multi-band photometry from optical and near-infrared surveys to confirm membership. Based on spectroscopic evidence for mass loss and the presence of circumstellar (CS) dust in their SEDs, we find that 30%-40% of the yellow supergiants are likely in a post-RSG state. Comparison with evolutionary tracks shows that these mass-losing, post-RSGs have initial masses between 20 and 40M_{sun}_. More than half of the observed RSGs in M31 and M33 are producing dusty CS ejecta. We also identify two new warm hypergiants in M31, J004621.05+421308.06 and J004051.59+403303.00, both of which are likely in a post-RSG state.
- ID:
- ivo://CDS.VizieR/J/ApJ/790/48
- Title:
- Variable stars in M31 & M33. II. LBVs
- Short Name:
- J/ApJ/790/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the luminous blue variables (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-supernova stages of very massive stars. We have begun a survey of the evolved and unstable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we review the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars. We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiescent or visual minimum state compared to the B-type supergiants and Of/WN stars which they spectroscopically resemble. The nature of the Fe II emission line stars and their relation to the LBV state remains uncertain, but some have properties in common with the warm hypergiants and the sgB[e] stars. Several individual stars are discussed in detail. We identify three possible candidate LBVs and three additional post-red supergiant candidates. We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor variable, but is a very luminous late O-type supergiant and one of the most luminous stars or pair of stars in M33.
