Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userColder and Hotter: Interferometric imaging of {beta} Cassiopeiae and {alpha} Leonis
184
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Near-infrared interferometers have recently imaged a number of rapidly rotating A-type stars, finding levels of gravity darkening inconsistent with theoretical expectations. Here, we present new imaging of both a cooler star {beta} Cas (F2IV) and a hotter one {alpha} Leo (B7V) using the CHARA array and the MIRC instrument at the H band. Adopting a solid-body rotation model with a simple gravity darkening prescription, we modeled the stellar geometric properties and surface temperature distributions, confirming both stars are rapidly rotating and show gravity darkening anomalies. We estimate the masses and ages of these rapid rotators on L-Rpol and HR diagrams constructed for non-rotating stars by tracking their non-rotating equivalents. The unexpected fast rotation of the evolved subgiant {beta} Cas offers a unique test of the stellar core-envelope coupling, revealing quite efficient coupling over the past ~ 0.5 Gyr. Lastly we summarize all our interferometric determinations of the gravity darkening coefficient for rapid rotators, finding none match the expectations from the widely used von Zeipel gravity darkening laws. Since the conditions of the von Zeipel law are known to be violated for rapidly rotating stars, we recommend using the empirically-derived {beta} = 0.19 for such stars with radiation-dominated envelopes. Furthermore, we note that no paradigm exists for self-consistently modeling heavily gravity-darkened stars that show hot radiative poles with cool convective equators.
rate research
Read More
V1022 Cas has been known as a spectroscopic binary for a century. It was found to be eclipsing based on photometry from the Hipparcos satellite, and an astrometric orbit was recently obtained from near-infrared interferometry. We present the first high-precision measurement of the radii of the stars based on light curves obtained by the TESS satellite. Combined with published radial velocities from high-resolution spectra, we measure the masses of the stars to be 1.626 +/- 0.001 Msun and 1.609 +/- 0.001 Msun, and the radii to be 2.591 +/- 0.026 Rsun and 2.472 +/- 0.027 Rsun. The 12.16-d orbit is eccentric and the stars rotate sub-synchronously, so the system is tidally unevolved. A good match to these masses and radii, and published temperatures of the stars, is found for several sets of theoretical stellar evolutionary models, for a solar metallicity and an age of approximately 2 Gyr. Four separate distance determinations to the system are available, and are in good agreement. The distances are based on surface brightness calibrations, theoretical bolometric corrections, the Gaia parallax, and the angular size of the astrometric orbit. A detailed spectroscopic analysis of the system to measure chemical abundances and more precise temperatures would be helpful.
Auns. The aim of our paper is to investigate the low-amplitude and long-period variations in evolved stars with a precise radial velocity (RV) survey. Methods. The high-resolution, the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from 2003 to 2013 for a radial velocity survey of giant stars as part of the exoplanet search program at Bohyunsan Optical Astronomy Observatory (BOAO). Results. We report the detection of three new planetary companions orbiting the K giants beta Cnc, mu Leo, and beta UMi. The planetary nature of the radial velocity variations is supported by analyzes of ancillary data. The HIPPARCOS photometry shows no variations with periods close to those in RV variations and there is no strong correlation between the bisector velocity span (BVS) and the radial velocities for each star. Furthermore, the stars show weak or no core reversal in Ca II H lines indicating that they are inactive stars. The companion to beta Cnc has a minimum mass of 7.8 M_Jup in a 605-day orbit with an eccentricity of 0.08. The giant mu Leo is orbited by a companion of minimum mass of 2.4 M_Jup having a period of 357 days and an eccentricity of 0.09. The giant beta UMi is a known barium star and is suspected of harboring a white dwarf or substellar mass companion. Its companion has a minimum mass of 6.1 M_Jup, a period of 522 days, and an eccentricity e = 0.19.
We combine nulling interferometry at 10 {mu}m using the MMT and Keck Telescopes with spectroscopy, imaging, and photometry from 3 to 100 {mu}m using Spitzer to study the debris disk around {beta} Leo over a broad range of spatial scales, corresponding to radii of 0.1 to ~100 AU. We have also measured the close binary star o Leo with both Keck and MMT interferometers to verify our procedures with these instruments. The {beta} Leo debris system has a complex structure: 1.) relatively little material within 1 AU; 2.) an inner component with a color temperature of ~600 K, fitted by a dusty ring from about 2 to 3 AU; and 3.) a second component with a color temperature of ~120 K fitted by a broad dusty emission zone extending from about ~5 AU to ~55 AU. Unlike many other A-type stars with debris disks, {beta} Leo lacks a dominant outer belt near 100 AU.
We report on K-band interferometric observations of the bright, rapidly rotating star Regulus (type B7 V) made with the CHARA Array on Mount Wilson, California. Through a combination of interferometric and spectroscopic measurements, we have determined for Regulus the equatorial and polar diameters and temperatures, the rotational velocity and period, the inclination and position angle of the spin axis, and the gravity darkening coefficient. These first results from the CHARA Array provide the first interferometric measurement of gravity darkening in a rapidly rotating star and represent the first detection of gravity darkening in a star that is not a member of an eclipsing binary system.
Optical interferometry is a powerful tool to investigate the close environment of AGB stars. With a spatial resolution of a few milli-arcseconds, it is even possible to image directly the surface of angularly large objects. This is of special interest forMira stars and red supergiants for which the dust-wind is initiated from or very close to the photosphere by an interplay between pulsation and convection. Based on two-epoch interferometric observations of the Mira star X Hya, we present how the variation of the angular size with wavelength challenges pulsation models and how reconstructed images can reveal the evolution of the object shape and of its asymmetric structures.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
