A Low-Resolution Spectroscopic Exploration of Puzzling OGLE Variable Stars (original) (raw)
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The ASAS-SN catalogue of variable stars IX: The spectroscopic properties of Galactic variable stars
Monthly Notices of the Royal Astronomical Society
The All-Sky Automated Survey for Supernovae provides long baseline (∼4 yr) V-band light curves for sources brighter than V≲ 17 mag across the whole sky. We produced V-band light curves for a total of ∼61.5 million sources and systematically searched these sources for variability. We identified ∼426 000 variables, including ∼219 000 new discoveries. Most (${\sim }74{ per\ cent}$) of our discoveries are in the Southern hemisphere. Here, we use spectroscopic information from LAMOST, GALAH, RAVE, and APOGEE to study the physical and chemical properties of these variables. We find that metal-poor eclipsing binaries have orbital periods that are shorter than metal-rich systems at fixed temperature. We identified rotational variables on the main-sequence, red giant branch, and the red clump. A substantial fraction (${\gtrsim }80{ per\ cent}$) of the rotating giants have large vvvrot or large near-ultraviolet excesses also indicative of fast rotation. The rotational variables have unusual a...
2010
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 onboard 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 (RRc) pulsators, and 5 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 day, 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 firstovertone 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 δ-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. We estimate the distance to IC 1613 using various methods based on the photometric and pulsational properties of the Cepheids and RR Lyrae stars. The values we find are in very good agreement with each other and with previous estimates based on independent methods. When corrected to a common reddening of E(B−V)=0.025 and true LMC distance modulus of (m−M) LMC,0 =18.515±0.085, we find that all the distance determinations from the literature converge to a common value of (m−M) 0 =24.400±0.014 (statistical), or 760 kpc. The parallel WFPC2 field, which lies within three core radii, was also searched for variable stars. We discovered nine RR Lyrae stars (4 RRab, 4 RRc and 1 RRd) and two Cepheids, even though the lower signal-to-noise ratio of the observations did not allow us to measure their periods as accurately as for the variables in the ACS field-of-view. We provide their coordinates and approximate properties for completeness.
Proceedings of the 41st Conference on Variable Stars Research
2010
In November 2009, another national conference on variable stars, stellar astrophysics in general and on extrasolar planets was organised by Variable Star and Exoplanet section of Czech Astronomical Society. The conference was held in beautiful and one of the oldest observatory in Czech republic - Stefanik Observatory in Prague. Our conferences on variable star research provide unique opportunities for meetings between professional and amateur astronomers and have become a crucial platform for exchanging information and sharing knowledge. These events help to keep the local astronomical community alive and active. This years conference was held on a weekend from November 27 to November 29. All almost 40 participants were able to witness the richness of our field and the joy that research on variable stars brings to our lifes.
Variable stars in stellar systems
We discuss in detail the pulsation properties of variable stars in globular clusters (GCs) and in Local Group (LG) dwarf galaxies. Data available in the literature strongly support the evidence that we still lack a complete census of variable stars in these stellar systems. This selection bias is even more severe for small-amplitude variables such as Oscillating Blue Stragglers (OBSs) and new exotic groups of variable stars located in crowded cluster regions. The same outcome applies to large-amplitude, long-period variables as well as to RR Lyrae and Anomalous Cepheids in dwarf galaxies.
Monthly Notices of the Royal Astronomical Society, 2016
We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey, a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0-and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find that many of these variables have spectra which are consistent with being δ Scuti-type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed followup studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the 'Bump Cepheid' phenomena in a δ Scuti star, with OW J175848.21-271653.7 showing a pronounced 22 per cent amplitude dip lasting 3 min during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.
Variability survey of brightest stars in selected OB associations
Astronomy & Astrophysics, 2017
Context. The stellar evolution theory of massive stars remains uncalibrated with high-precision photometric observational data mainly due to a small number of luminous stars that are monitored from space. Automated all-sky surveys have revealed numerous variable stars but most of the luminous stars are often overexposed. Targeted campaigns can improve the time base of photometric data for those objects. Aims. The aim of this investigation is to study the variability of luminous stars at different timescales in young open clusters and OB associations. Methods. We monitored 22 open clusters and associations from 2011 to 2013 using a 0.25-m telescope. Variable stars were detected by comparing the overall light-curve scatter with measurement uncertainties. Variability was analysed by the light curve feature extraction tool FATS. Periods of pulsating stars were determined using the discrete Fourier transform code SigSpec. We then classified the variable stars based on their pulsation periods and available spectral information. Results. We obtained light curves for more than 20 000 sources of which 354 were found to be variable. Amongst them we find 80 eclipsing binaries, 31 α Cyg, 13 β Cep, 62 Be, 16 slowly pulsating B, 7 Cepheid, 1 γ Doradus, 3 Wolf-Rayet and 63 late-type variable stars. Up to 55% of these stars are potential new discoveries as they are not present in the Variable Star Index (VSX) database. We find the cluster membership fraction for variable stars to be 13% with an upper limit of 35%.
Variable stars in nearby galaxies. III. White light observations of Field B of IC 1613
Astronomy and Astrophysics, 2000
Two nearby galaxies, IC 1613 and NGC 6822, were observed over four years to detect short period Cepheids and to obtain good light curves for Fourier decomposition. Since the program was carried out with a relatively small telescope, the Dutch 0.9 m at ESO-La Silla, the observations were performed without filter (white light), or Wh-band; the advantage of this technique is that the photon statistics correspond to those of V-band observations of similar exposure time obtained with a 2-m class telescope. In this paper we discuss some properties of Wh photometry and present the results of the observations of Field B in IC 1613 (3.8'x3.8'). A total of 65 images were obtained and the reduction was performed with DAOPHOT. The light curves of 4037 stars were measured, and the analysis using various techniques allowed the detection of 121 variable stars. We detected 51 population I Cepheids, while previously only 12 Cepheids were known in the same field. Most of these have short periods and some are first overtone mode pulsators. The other variable stars include one eclipsing binary, two suspected W Vir stars, 57 irregular and semi-regular red variables, 3 periodic red variables and 6 irregular blue variables. Based on observations collected at ESO-La Silla
Variable Stars and Galactic Structure
2013
Variable stars have a unique part to play in Galactic astronomy. Among the most important of these variables are the Cepheids (types I and II), the RR Lyraes and the Miras (O- and C-rich). The current status of the basic calibration of these stars in their roles as distance, structure and population indicators is outlined and some examples of recent applications of these stars to Galactic and extragalactic problems is reviewed. The expected impact of Gaia on this type of work is discussed and the need for complementary ground based observations, particularly large scale near-infrared photometry, is stressed.
A survey for variable young stars with small telescopes: First results from HOYS-CAPS
Monthly Notices of the Royal Astronomical Society, 2018
Variability in young stellar objects (YSOs) is one of their primary characteristics. Long-term, multifilter, high-cadence monitoring of large YSO samples is the key to understand the partly unusual light curves that many of these objects show. Here we introduce and present the first results of the HOYS-CAPS citizen science project that aims to perform such monitoring for nearby (d < 1 kpc) and young (age < 10 Myr) clusters and star-forming regions, visible from the northern hemisphere, with small telescopes. We have identified and characterized 466 variable (413 confirmed young) stars in eight young, nearby clusters. All sources vary by at least 0.2 mag in V, have been observed at least 15 times in V, R, and I in the same night over a period of about 2 yr, and have a Stetson index of larger than 1. This is one of the largest samples of variable YSOs observed over such a time span and cadence in multiple filters. About two-thirds of our sample are classical T-Tauri stars, while the rest are objects with depleted or transition discs. Objects characterized as bursters show by far the highest variability. Dippers and objects whose variability is dominated by occultations from normal interstellar dust or dust with larger grains (or opaque material) have smaller amplitudes. We have established a hierarchical clustering algorithm based on the light-curve properties that allows the identification of the YSOs with the most unusual behaviour and to group sources with similar properties. We discuss in detail the light curves of the unusual objects V2492 Cyg, V350 Cep, and 2MASS J21383981+5708470.