arXiv subjects

Laszlo Sturmann

Publications and source records attributed to Laszlo Sturmann.

42 records · Page 3Linked to original sources

arXiv2008

The Visual Orbit of the 1.1-day Spectroscopic Binary σ^2 Coronae Borealis from Interferometry at the CHARA Array

We present an updated spectroscopic orbit and a new visual orbit for the double-lined spectroscopic binary σ^2 Coronae Borealis based on radial velocity measurements at the Oak Ridge Observatory in Harvard, Massachusetts and interferometric visibility measurements at the CHARA Array on Mount Wilson. σ^2 CrB is composed of two Sun-like stars of roughly equal mass in a circularized orbit with a period of 1.14 days. The long baselines of the CHARA Array have allowed us to resolve the visual orbit for this pair, the shortest period binary yet resolved interferometrically, enabling us to determine component masses of 1.137 \pm 0.037 M_sun and 1.090 \pm 0.036 M_sun. We have also estimated absolute V-band magnitudes of MV (primary) = 4.35 \pm 0.02 and MV(secondary) = 4.74 \pm 0.02. A comparison with stellar evolution models indicates a relatively young age of 1-3 Gyr, consistent with the high Li abundance measured previously. This pair is the central component of a quintuple system, along with another similar-mass star, σ^1 CrB, in a ~ 730-year visual orbit, and a distant M-dwarf binary, σCrB C, at a projected separation of ~ 10 arcmin. We also present differential proper motion evidence to show that components C & D (ADS 9979C & D) listed for this system in the Washington Double Star Catalog are optical alignments that are not gravitationally bound to the σCrB system.

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arXiv2008

The radii of the nearby K5V and K7V stars 61 Cyg A & B - CHARA/FLUOR interferometry and CESAM2k modeling

Context: The main sequence binary star 61 Cyg (K5V+K7V) is our nearest stellar neighbour in the northern hemisphere. This proximity makes it a particularly well suited system for very high accuracy interferometric radius measurements. Aims: Our goal is to constrain the poorly known evolutionary status and age of this bright binary star. Methods: We obtained high accuracy interferometric observations in the infrared K' band, using the CHARA/FLUOR instrument. We then computed evolutionary models of 61 Cyg A & B with the CESAM2k code. As model constraints, we used a combination of observational parameters from classical observation methods (photometry, spectroscopy) as well as our new interferometric radii. Results: The measured limb darkened disk angular diameters are theta_LD(A) = 1.775 +/- 0.013 mas and theta_LD(B) = 1.581 +/- 0.022 mas, respectively for 61 Cyg A and B. Considering the high accuracy parallaxes available, these values translate into photospheric radii of R(A) = 0.665 +/- 0.005 Rsun and R(B) = 0.595 +/- 0.008 Rsun. The new radii constrain efficiently the physical parameters adopted for the modeling of both stars, allowing us to predict asteroseismic frequencies based on our best-fit models. Conclusions: The CESAM2k evolutionary models indicate an age around 6 Gyrs and are compatible with small values of the mixing length parameter. The measurement of asteroseismic oscillation frequencies in 61 Cyg A & B would be of great value to improve the modeling of this important fiducial stellar system, in particular to better constrain the masses.

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arXiv2008

Angular Diameters of the G Subdwarf $μ$ Cassiopeiae A and the K Dwarfs $σ$ Draconis and HR 511 from Interferometric Measurements with the CHARA Array

Using the longest baselines of the CHARA Array, we have measured the angular diameter of the G5 V subdwarf $μ$ Cas A, the first such determination for a halo population star. We compare this result to new diameters for the higher metallicity K0 V stars, $σ$ Dra and HR 511, and find that the metal-poor star, $μ$ Cas A, has an effective temperature ($T_{\rm eff}=5297\pm32$ K), radius ($R=0.791\pm0.008 R_{\rm \odot}$), and absolute luminosity ($L=0.442\pm0.014 L_{\rm \odot}$) comparable to the other two stars with later spectral types. We show that stellar models show a discrepancy in the predicted temperature and radius for $μ$ Cas A, and we discuss these results and how they provide a key to understanding the fundamental relationships for stars with low metallicity.

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arXiv2008

The Search for Stellar Companions to Exoplanet Host Stars Using the CHARA Array

Most exoplanets have been discovered via radial velocity studies, which are inherently insensitive to orbital inclination. Interferometric observations will show evidence of a stellar companion if it sufficiently bright, regardless of the inclination. Using the CHARA Array, we observed 22 exoplanet host stars to search for stellar companions in low-inclination orbits that may be masquerading as planetary systems. While no definitive stellar companions were discovered, it was possible to rule out certain secondary spectral types for each exoplanet system observed by studying the errors in the diameter fit to calibrated visibilities and by searching for separated fringe packets.

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arXiv2008

CHARA Array Measurements of the Angular Diameters of Exoplanet Host Stars

We have measured the angular diameters for a sample of 24 exoplanet host stars using Georgia State University's CHARA Array interferometer. We use these improved angular diameters together with Hipparcos parallax measurements to derive linear radii and to estimate the stars' evolutionary states.

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arXiv2005

The projection factor of delta Cephei A calibration of the Baade-Wesselink method using the CHARA Array

Cepheids play a key role in astronomy as standard candles for measuring intergalactic distances. Their distance is usually inferred from the Period-Luminosity relationship, calibrated using the semi-empirical Baade-Wesselink method. Using this method, the distance is known to a multiplicative factor, called the projection factor. Presently, this factor is computed using numerical models - it has hitherto never been measured directly. Based on our new interferometric measurements obtained with the CHARA Array and the already published parallax, we present a geometrical measurement of the projection factor of a Cepheid, delta Cep. The value we determined, p = 1.27$\pm$0.06, confirms the generally adopted value of p = 1.36 within 1.5 sigmas. Our value is in line with recent theoretical predictions of Nardetto et al. (2004).

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