Search results for "K-type main-sequence star"
showing 10 items of 23 documents
Study of a sample of faint Be stars in the exofield of CoRoT
2013
International audience; Context. Be stars are probably the most rapid rotators among stars in the main sequence (MS) and, as such, are excellent candidates to study the incidence of the rotation on the characteristics of their non-radial pulsations, as well as on their internal structure. Pulsations are also thought to be possible mechanisms that help the mass ejection needed to build up the circumstellar disks of Be stars.Aims. The purpose of this paper is to identify a number of faint Be stars observed with the CoRoT satellite and to determine their fundamental parameters, which will enable us to study their pulsation properties as a function of the location in the HR diagram and to searc…
In-flight calibration of the ROSAT HRI ultraviolet sensitivity
2000
Comparing measured and estimated count rates of a few selected sample stars, we confirm the validity and provide the in-flight calibration of the ROSAT HRI UV/visible effective area model in Zombeck et al. The count rate estimates for Betelgeuse derived with this model are in agreement with the measured HRI upper limit. This result is also confirmed in an erratum by Berghöfer et al. aimed at revising their previous calculation, which was overestimated by more than 2 orders of magnitude. Adopting this ROSAT HRI UV/visible effective area model and measured UV/visible spectra of a set of sample stars covering the range of Teff 3000-40,000 K, we have built the calibration curves to estimate UV/…
Viewing the Sun as an X-ray star
2003
The Sun is the late-type star we can study with the highest level of detail. In the interpretation of stellar data, therefore, it is often assumed that the physical processes of the coronae of late-type stars are similar to those of the solar corona, i.e. the "solar-stellar analogy". In order to investigate the validity of this assumption, we have started a program to study systematically the Sun as an X-ray star. Our program aims to explore how far the solar model can be applied to other stars. In this paper we review the results obtained from these studies and, in particular, we discuss the variability of a star identical to the Sun during its cycle, the contribution of different coronal …
The chemical composition of extremely metal-poor and carbon-rich star HD 112869
2005
The preliminary results of abundance analysis are presented for extremely metal-poor carbon star HD 112869 = TT CVn = CGCS 3319. The radial velocity was found to be −137.7 km s −1 . Our LTE abundance analysis supports an extremely low metallicity for TT CVn, [Fe/H] = −3.2, and a significant overabundance of carbon and neutron-capture elements. The 12 C/ 13 C ratio in the atmosphere of HD 112869 is high.
Lithium in metal-poor red giants
2009
AbstractThe lithium abundance was calculated for five metal-poor red giant stars from Li i doublet at 6707 Å by fitting the observed high-resolution spectra with synthetic spectra. The lithium abundance was found to be low in all stars, logϵ(Li) ≤ 1.8, confirming lithium depletion on the red giant and asymptotic giant branch.
The cool Galactic R Coronae Borealis variable DY Persei
2005
Results of first CCD photometry during the recent deep light decline, and high-resolution spectroscopy, are presented for DY Persei. The spectra show variable blueshifted features in the sodium D lines. The C lines are strong whereas neutron- capture elements are not enhanced. The isotopic 13 CN(2, 0) lines relative to 12 CN are of similar strength with those for the carbon star U Hya. All these confirm the RCB nature of DY Per and the existence of ejected clouds. At least two clouds are revealed at −197.3 and −143.0 km s −1 . A star was detected about 0. 4t o the west and 2 . 5 to the north from DY Per. This anonymous companion, with observed colour indices (B − V) = 0.68 and (V − R) � 1…
Be stars in open clusters. I. uvby $ ^{\bf \beta}$ photometry
1996
We present uvby β photometry for Be stars in eight open clusters and two OB associations. It is shown that Be stars occupy anomalous positions in the photometric diagrams, which can be explained in terms of the circumstellar continuum radiation contribution to the photometric indices. In the - M V plane Be stars appear redder than the non emission B stars, due to the additional reddening caused by the hydrogen free-bound and free-free recombination in the circumstellar envelope. In the c 0 - M V plane the earlier Be stars present lower c 0 values than absorption-line B stars, which is caused by emission in the Balmer discontinuity, while the later Be stars deviate towards higher c 0 values,…
HD 50975: a yellow supergiant in a spectroscopic binary system
2014
Context. Recent detection of a yellow supergiant star as a possible progenitor of a supernova has posed serious questions about our understanding of the evolution of massive stars. Aims. The spectroscopic binary star HD 50975 with an unseen hot secondary was studied in detail with the main goal of estimating fundamental parameters of both components and the binary system. Methods. A comprehensive analysis and modeling of collected long-term radial velocity measurements, photometric data, and spectra was performed to calculate orbital elements, atmospheric parameters, abundances, and luminosities. The spectrum in an ultraviolet region was studied to clarify the nature of an unseen companion …
Four colour photometry of binary systems
1998
This paper presents new uvby light curves of the detached eclipsing binary CR Cas together with some H measurements. From the analysis of the photometry we have estimated preliminary values for interstellar red- dening and distance, radiative parameters of both compo- nents and an approximation to the geometrical elements of the system. The intrinsic photometric indices are com- patible with spectral types B0.5V + B1V.
Activity and Rotation in the Young Cluster h Per
2013
We study the stellar rotation-activity relation in the crucial age at which stars reach the fastest rotation. To this aim we have analyzed data of the young cluster h Per, very rich and compact, located at 2300 pc, that at an age of 13 Myr should be mainly composed of stars that have ended their contraction phase and that have not lost significant angular momentum viamagnetic breaking. To constrain the activity level of h Per members we have analyzed a deep Chandra/ACIS-I observation. Rotational periods of h Per members have been derived by Moraux et al. (2013) in the framework of the MONITOR project (Aigrain et al. 2007; Irwin et al. 2007). In the Chandra observation we have detected 1010 …