- ID:
- ivo://CDS.VizieR/J/AJ/130/776
- Title:
- Secular evolution in Mira variable pulsations
- Short Name:
- J/AJ/130/776
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present the results of our study of period change in 547 Mira variables using data from the AAVSO (American Association of Variable Star Observers). We use wavelet analysis to measure the period changes in individual Mira stars over the span of available data. By making linear fits to the period versus time measurements, we determine the average rates of period change, d(lnP)/dt, for each of these stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/147/140
- Title:
- SED of 24 class I and class II FU Orionis stars
- Short Name:
- J/AJ/147/140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- FU Orionis stars (FUors) are eruptive pre-main sequence objects thought to represent quasi-periodic or recurring stages of enhanced accretion during the low-mass star-forming process. We characterize the sample of known and candidate FUors in a homogeneous and consistent way, deriving stellar and circumstellar parameters for each object. We emphasize the analysis in those parameters that are supposed to vary during the FUor stage. We modeled the spectral energy distributions of 24 of the 26 currently known FUors, using the radiative transfer code of Whitney et al. We compare our models with those obtained by Robitaille et al. for Taurus class II and I sources in quiescence periods by calculating the cumulative distribution of the different parameters. FUors have more massive disks: we find that ~80% of the disks in FUors are more massive than any Taurus class II and I sources in the sample. Median values for the disk mass accretion rates are ~10^-7^M_{sun}_/yr versus ~10^-5^M_{sun}_/yr for standard young stellar objects (YSOs) and FUors, respectively. While the distributions of envelope mass accretion rates for class I FUors and standard class I objects are similar, FUors, on average, have higher envelope mass accretion rates than standard class II and class I sources. Most FUors (~70%) have envelope mass accretion rates above 10^-7^M_{sun}_/yr. In contrast, 60% of the classical YSO sample has an accretion rate below this value. Our results support the current scenario in which changes experimented by the circumstellar disk explain the observed properties of these stars. However, the increase in the disk mass accretion rate is smaller than theoretically predicted, although in good agreement with previous determinations.
- ID:
- ivo://CDS.VizieR/J/A+A/656/A66
- Title:
- Semi-regular red giants as distance indicators
- Short Name:
- J/A+A/656/A66
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Semi-regular variables (SRVs) are similar to Miras in brightness, and they also follow PLRs, though not necessarily the same as Miras. As potential standard candles they are more challenging than Miras due to their smaller variability amplitudes and less regular light curves, but they are substantially more numerous and especially promising to probe old stellar populations. We aim to characterize the variability of SRVs, with focus on their connection with Miras, in order to prepare the ground for investigating their potential as distance indicators. We examine SRVs and Miras in the Magellanic Clouds from OGLE-III observations, with data from Gaia and 2MASS. After cleaning the sample from variability periods unrelated to pulsation, we classify each source by chemical type and combination of pulsation modes. We examine the results in terms of global photometric and pulsation properties. We identify four SRVs groups that fit the general evolutionary scenario predicted by theory. SRVs dominated by fundamental-mode pulsation are very similar to Miras, especially if mono-periodic. They further split into two sub-groups, one of which follows the same sequence as Miras in the period-luminosity and period-amplitude diagram, without discontinuity. The similarities between Miras and SRVs suggest that the latter can be adopted as complementary distance indicators to the former, thereby at least doubling the available number of LPVs suitable for use as distance indicators. The traditional amplitude-based separation between Miras and SRVs is not necessarily appropriate, and a more physically sound criterion should also involve pulsation periods. While this would require comparatively longer time series, they are expected to become accessible in the coming years even for weak sources thanks to current and future large-scale surveys. The table of reclassified LPVs is made public.
- ID:
- ivo://CDS.VizieR/J/A+A/296/727
- Title:
- Semiregular variables H2O maser
- Short Name:
- J/A+A/296/727
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 107 semiregular variables of spectral type M have been observed in the H2O 6(16)-5(23) line at 22.235GHz with the 100m Effelsberg radio telescope and maser emission has been detected in 23 objects, of which 10 are new detections.
- ID:
- ivo://CDS.VizieR/J/ApJ/552/289
- Title:
- Semiregular variable stars in Baade's windows
- Short Name:
- J/ApJ/552/289
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By cross-correlating the results of two recent large-scale surveys, the general properties of a well-defined sample of semiregular variable stars have been determined. ISOGAL mid-infrared photometry (7 and 15{mu}m and MACHO V and R light curves are assembled for approximately 300 stars in the Baade's windows of low extinction toward the Galactic bulge. These stars are mainly giants of late M spectral type, evolving along the asymptotic giant branch (AGB). They are found to possess a wide and continuous distribution of pulsation periods and to obey an approximate logP-M_bol_ relation or set of such relations.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A63
- Title:
- Semi-sinusoidal variability with CoRoT
- Short Name:
- J/A+A/555/A63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To date, the CoRoT space mission has produced more than 124471 light curves. Classifying these curves in terms of unambiguous variability behavior is mandatory for obtaining an unbiased statistical view on their controlling root-causes. The present study provides an overview of semi-sinusoidal light curves observed by the CoRoT exo-field CCDs. We selected a sample of 4206 light curves presenting well-defined semi-sinusoidal signatures. The variability periods were computed based on Lomb-Scargle periodograms, harmonic fits, and visual inspection.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A6
- Title:
- Seven new pulsating sdA stars
- Short Name:
- J/A+A/617/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of the recently identified "sdA" spectroscopic class of star is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravities intermediate to main sequence stars and isolated white dwarfs, and effective temperatures below the lower limit for He-burning subdwarfs. Most are likely products of binary stellar evolution, whether extremely low-mass white dwarfs and their precursors, or blue stragglers in the halo. Stellar eigenfrequencies revealed through time series photometry of pulsating stars sensitively probe stellar structural properties. The properties of pulsations exhibited by any sdA stars would contribute importantly to our developing understanding of this class. We extend our photometric campaign to discover pulsating extremely low-mass white dwarfs from McDonald Observatory to target sdA stars classified from SDSS spectra. We also obtain follow-up time series spectroscopy to search for binary signatures from four new pulsators. Out of 23 sdA stars observed, we clearly detect stellar pulsations in seven. Dominant pulsation periods range from 4.6 minutes to 12.3 hours, with most on hour timescales. We argue specific classifications for some of the new variables, identifying both compact and likely main sequence dwarf pulsators, along with a candidate low-mass RR Lyrae star. With dominant pulsation periods spanning orders of magnitude, the pulsational evidence supports the emerging narrative that the sdA class consists of multiple stellar populations. Since multiple types of sdA exhibit stellar pulsations, follow-up asteroseismic analysis can be used to probe the precise evolutionary natures and stellar structures of these individual subpopulations.
- ID:
- ivo://CDS.VizieR/J/AJ/111/902
- Title:
- Short-period Cepheids
- Short Name:
- J/AJ/111/902
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UBVRI data on 36 short-period (P<5days) Cepheids is given. The observing techniques and reduction procedures are described. A consistent set of finding charts, a set of standard stars for each Cepheid, and improved coordinates are also presented.
- ID:
- ivo://CDS.VizieR/J/AJ/158/68
- Title:
- Short-period variables in young open cluster Stock 8
- Short Name:
- J/AJ/158/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present time-series photometry in the field of Stock 8 and identified 130 short-period variable stars. Twenty-eight main-sequence and 23 pre-main-sequence variables are found to be part of cluster Stock 8. The main-sequence variables are classified as slow pulsators of the B-type, {beta} Cep, and {delta} Scuti stars. Fourteen main-sequence stars could be new class variables as discussed by Mowlavi et al. (2013, J/A+A/554/A108) and Lata et al. (2011MNRAS.418.1346L; 2012MNRAS.427.1449L; 2014, J/MNRAS/442/273; 2016MNRAS.456.2505L). The age and mass of pre-main-sequence variables are found to be ~<5 Myr and in the mass range of 0.5-2.8 M_{sun}_, respectively. These pre-main-sequence stars could be T-Tauri variables. We have found 5 and 2 of 23 pre-main-sequence variables as classical T-Tauri stars and Herbig Ae/Be stars, respectively, whereas 16 pre-main-sequence stars are classified as weak-line T-Tauri stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/385
- Title:
- Short-period variables near Galactic Centre
- Short Name:
- J/MNRAS/429/385
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the result of our near-infrared survey of short-period variable stars (P<60d) in a field of view of 20'x30' towards the Galactic Centre (GC). Forty-five variables are discovered and we classify the variables based on their light-curve shapes and other evidence. In addition to 3 classical Cepheids reported previously, we find 16 type II Cepheids, 24 eclipsing binaries, 1 pulsating star with P=0.265d (RR Lyr or {delta} Sct) and 1 Cepheid-like variable whose nature is uncertain. Eclipsing binaries are separated into the foreground objects and those significantly obscured by interstellar extinction. One of the reddened binaries contains an O-type supergiant and its light curve indicates an eccentric orbit. We discuss the nature and distribution of type II Cepheids as well as the distance to the GC based on these Cepheids and other distance indicators. The estimates of R_0_(GC) we obtained based on photometric data agree with previous results obtained with kinematics of objects around the GC. Furthermore, our result gives support to the reddening law obtained by Nishiyama and collaborators, A_Ks_/E(H-Ks)=1.44, because a different reddening law would result in a rather different distance estimate.
