Doradus Variables Research Articles

Time Series Photometry of Variable Stars in the Globular Cluster NGC 6397

Time series BVI photometry is presented for 16 short-period variables located in the central region of the globular cluster NGC 6397. The sample includes 9 newly detected variables. The light curve of cataclysmic variable CV6 shows variability with a period of 0.2356 days. We confirm an earlier reported period of 0.472 days for cataclysmic variable CV1. Phased light curves of both CVs exhibit sine-like light curves, with two minima occurring during each orbital cycle. The secondary component of CV1 has a low average density of 0.83 g/cm^{3} indicating that it cannot be a normal main sequence star. Variables among the cluster blue stragglers include a likely detached eclipsing binary with orbital period of 0.787 days, three new SX Phe stars (one of which has the extremely short period of 0.0215 days), and three low amplitude variables which are possible gamma Doradus variables.

Evidence of the γ Doradus nature for a group of candidates

We present in this paper new photometry of eight stars suspected to be γ Doradus variables according to Handler & Kaye (2000). The new observational material has been analyzed and previously published data re-analyzed by means of an objective period search technique, based on the least-squares algorithm, called Multifre (Bossi & Nuñez 2002). We found evidence for the inclusion of seven of these stars in the list of recognized γ Doradus variables.

The Orbit and Pulsation Periods of the γ Doradus Variable HR 6844 (V2502 Ophiuchi)

We obtained spectroscopic and photometric observations of the γ Doradus variable HR 6844 (=V2502 Ophiuchi). Radial velocities show that this star is a single-lined binary with a period of 4.4852 days. The primary is an F1 V star, while the secondary is likely an M dwarf. Velocity residuals to a circular orbit have a period of 1.3071 days and an amplitude of ~3 km s-1. Three periods of light variation were detected, 1.30702, 1.4350, and 0.62286 days. The first period is essentially identical to that found in the radial velocities and has the largest amplitude, a peak-to-peak value of 0.067 mag in B. The photometric check star, 73 Oph (=HR 6795), has light variations with a period of 0.61439 in B. Although the star is a close visual binary, the light variations are ascribed to the primary, making it most likely a newly discovered γ Doradus variable.

Six New γ Doradus Stars

ABSTRACTWe present high‐resolution spectroscopy and precision photometry of six new γ Doradus stars, one of which was independently discovered by another group. This brings the total number of confirmed γ Doradus variables to 30. All six of these variables fall in the spectral class range F0–F2; all but one are subgiants. The six stars have between one and five photometric periods in the range 0.3–1.2 days. We find no evidence for higher frequency δ Scuti pulsations in any of these six stars. Our spectroscopic observations reveal HD 108100 to be the first confirmed γ Doradus variable with composite broad and narrow line profiles suggesting the presence of a circumstellar shell or disk. HD 221866 has the most asymmetric absorption lines of the six stars in this paper and also the largest photometric amplitude. Most of the 30 confirmed γ Doradus variables lie in a fairly tight region of the H‐R diagram on or just above the main sequence that partially overlaps the cool edge of the δ Scuti instability strip. However, three stars, including two of the new variables in this paper, are subgiants that lie well within the δ Scuti strip. Among the 30 confirmed γ Doradus variables, we find no correlation between the photometric periods and intrinsic color, absolute magnitude, or luminosity.

Search for New γ Doradus Variable Stars in Open Clusters: Praesepe and α Persei

AbstractPhotometric observations of A-F stars in the uvbyβ system have been performed in order to detect γ Doradus variables in open clusters of different ages. In the clusters Praesepe and α Per, several stars show some type of variability but only three of them, KW370 (Praesepe) and HE104 and HE876 (α Per), can be classified as γ Doradus-type pulsators.

Driving g-Mode Pulsation in γ Doradus Variables

AbstractSurface convection zones in γ Doradus variables (early F-type g-mode pulsators) can drive pulsation via the ‘convective driving’ mechanism. This mechanism is first proposed and studied in the context of ZZ Cetis (hydrogen-envelope white dwarfs with g-mode pulsations) by Brickhill (1991) and Goldreich & Wu (1999). We implement and develop the convective driving theory to suit the environments on γ Dors, in particular, stronger super-adiabatic gradient and weaker convective flux than those in white dwarfs. This results in a spectrum of gravity-modes being excited in the observed temperature range. However, there are more remaining problems than those that are solved.

Observation of γ Doradus Stars in the Space Asteroseismology Era

AbstractAlmost 10 years have passed since the first claims of the existence of a new class of slowly pulsating variables near the cool border of δ Scuti instability strip. The consolidated class of γ Doradus variables faces now the challenge of space. In this paper, we review the most recent theoretical and observational results of these stars and we discuss how our knowledge of their nature will benefit from data collected in the forthcoming space-borne asteroseismological missions.

10 New γ Doradus and δ Scuti Stars

We present high-resolution spectroscopy and precision photometry of five new γ Doradus and five new δ Scuti variables. The five new γ Doradus variables substantially increase the number of confirmed stars of this class. All 10 stars fall in the spectral class range F0–F2, but they are cleanly separated into two groups by their luminosity and photometric periods. However, the period gap between the γ Doradus and δ Scuti stars is becoming very narrow since we confirm that HD 155154 is a γ Doradus star with the shortest periods reported to date (the shortest of its four periods is ∼0.312 days). We do not find any evidence in our sample for stars exhibiting both δ Scuti– and γ Doradus–type pulsations.

HR 8799: A Link between γ Doradus Variables and λ Bootis Stars

On the basis of a new classification-resolution spectrum, we find that HR 8799, a known member of the newly discovered γ Doradus variable star class, is a λ Bootis star. Spectral synthesis, in conjunction with fluxes from visible spectrophotometry and the TD-1 satellite, yields Teff = 7430 K, log g = 4.35, microturbulent velocity ξt = 2.7 km s-1, and metallicity [M/H] = -0.47 for HR 8799, confirming its metal-weak nature. HR 8799 is also a Vega-like star in that it shows excess flux at 60 μm, probably due to a circumstellar dust shell or disk. Thus, this star links three astrophysically interesting classes of stars and may provide potentially important constraints on the physics of, and the interconnections between, the λ Bootis phenomenon and the γ Doradus pulsation phenomenon.

HD 62454 and HD 68192: Two New γ Doradus Variables

We present multilongitude, multicolor photometry and simultaneous high-resolution, high signal-to-noise spectroscopy of the newly discovered γ Doradus variables HD 62454 and HD 68192. From combined Johnson and Stromgren data, we are able to identify five independent periods in HD 62454 and two stable periods in HD 68192. The data presented are sufficient to rule out all physically meaningful types of variations, with the one exception of the high-order, low-degree, nonradial gravity-mode pulsations that are believed to be at work in γ Doradus stars. We also find that HD 62454 is a double-lined spectroscopic binary and we present an orbital solution.

What are LBV’s? — Their characteristics and role in the upper H-R diagram

Only ten years ago a symposium on the special class of stars we now call Luminous Blue Variables (LBV’s) would not have been possible. At that time we were only just beginning to recognize the similarities among the stars we call S Doradus variables, P Cygni stars, and Hubble-Sandage variables, and their importance in the evolution of the most massive stars.About a decade ago it became clear that the observed H-R diagram has an upper luminosity limit and thatηCar, P Cyg, and S Dor are all near the temperature-dependent boundary for hot stars. With hindsight the luminosity boundary can be seen in an H-R diagram for hot stars published by Hutchings (1976), but the full temperature range is necessary to show that it really exists. When more data became available in 1977—1978, including the evolved and cool supergiants, the upper luminosity limit became obvious; and we proposed that an instability causingrapidandunsteadymass loss (i.e., LBV’s) is the basic reason for this boundary (Humphreys and Davidson 1979). We emphasized the temperature-dependence of the boundary for the most luminous hot stars, the lack of cooler counterparts at similar luminosities, the nearly temperature-independent limit to the luminosities of cool hypergiants, and the critical role that objects likeηCar, P Cyg, and S Dor may play in the evolution of the most massive stars.

Spectrophotometry of two luminous variable stars in the Andromeda Galaxy

view Abstract Citations (24) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometry of two luminous variable stars in the Andromeda galaxy. Gallagher, J. S. ; Kenyon, S. J. ; Hege, E. K. Abstract The spectrophotometry of two S Doradus variables in M31, AF Andromedae and A-1 Andromedae, shows that H Balmer, He I, Fe II, and Fe II forbidden line emissions dominate the spectra, with only Na D appearing in absorption. An analysis of the Fe II, Fe II forbidden line and He I line strengths leads to a model in which a star hotter than about 25,000 K is surrounded by an extensive envelope, with an implied mass loss rate of about 0.00005 solar masses/year. These figures, the environments, and the approximately 10 times lower luminosity suggest that these stars are not necessarily produced by the same mechanism as Eta Carinae. The evolution of a massive star to its core helium-burning phase may provide a model for the current status of A-1 And, while AF And's position in an interarm region of M31 supports a binary interpretation. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159262 Bibcode: 1981ApJ...249...83G Keywords: Andromeda Galaxy; Stellar Luminosity; Stellar Spectra; Stellar Spectrophotometry; Supergiant Stars; Variable Stars; Emission Spectra; H Lines; Helium; Stellar Envelopes; Stellar Mass Ejection; Astronomy full text sources ADS | data products SIMBAD (3) NED (1)