arXiv subjects

Ansgar Reiners

Publications and source records attributed to Ansgar Reiners.

111 records · Page 7Linked to original sources

arXiv2005

Discovery of an M4 Spectroscopic Binary in Upper Scorpius: A Calibration Point for Young Low-Mass Evolutionary Models

We report the discovery of a new low-mass spectroscopic (SB2) stellar binary system in the star-forming region of Upper Scorpius. This object, UScoCTIO5, was discovered by Ardila (2000), who assigned it a spectral class of M4. A KeckI HIRES spectrum revealed it to be double-lined, and we then carried out a program at several observatories to determine its orbit. The orbital period is 34 days, and the eccentricity is nearly 0.3. The importance of such a discovery is that it can be used to help calibrate evolutionary models at low masses and young ages. This is one of the outstanding problems in the study of formation mechanisms and initial mass functions at low masses. The orbit allows us to place a lower limit of 0.64 +- 0.02 M_sol on the total system mass. The components appear to be of almost equal mass. We are able to show that this mass is significantly higher than predicted by evolutionary models for an object of this luminosity and age, in agreement with other recent results. More precise determination of the temperature and surface gravity of the components would be helpful in further solidifying this conclusion.

astro-ph↗

arXiv2004

Altair's inclination from line profile analysis

We present a detailed spectroscopic study of line broadening in the A7IV-V star Altair. In a wavelength region covering 690AA we reconstruct the overall broadening profile taking into account more than 650 spectral lines. From the broadening profile we determine the projected rotational velocity vsini, derive an upper limit for the equatorial velocity v from the shape of the profile and search for signatures of differential rotation. Our redetermined value of vsini is (227 +-11)km/s. Measuring the first two zeros of the Fourier transformed broadening profile yield no signatures of differential rotation. We derive that Altair is seen under an inclination angle higher than i=68deg and it rotates at v<245km/s or slower than 53% of breakup velocity on a 1sigma level.

astro-ph↗

arXiv2003

The effects of inclination, gravity darkening and differential rotation on absorption profiles of fast rotators

Mechanisms influencing absorption line profiles of fast rotating stars can be sorted into two groups; (i) intrinsic variations sensitive to temperature and pressure, and (ii) global effects common to all spectral lines. I present a detailed study on the latter effects focusing on gravity darkening and inclination for various rotational velocities and spectral types. It is shown that the line shapes of rapidly and rigidly rotating stars mainly depend on the equatorial velocity $v_{\rm e}$, not on the projected rotational velocity $v \sin{i}$ which determines the lines width. The influence of gravity darkening and spectral type on the line profiles is shown. The results demonstrate the possibility of determining the inclination angle $i$ of single fast rotators, and they show that constraints on gravity darkening can be drawn for stellar samples. While significant line profile deformation occurs in stars rotating as fast as $v_{\rm e} \ga 200$ km s$^{-1}$, for slower rotators profile distortion are marginal. In these cases spectral signatures induced by, e.g., differential rotation are not affected by gravity darkening and the methods applicable to slow rotators can be applied to these faster rotators, too.

astro-ph↗