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Late-type Stars (late-type + star)
Selected AbstractsZeeman-Doppler imaging of late-type stars: The surface magnetic field of II PegASTRONOMISCHE NACHRICHTEN, Issue 10 2007T. A. Carroll Abstract Late-type stars in general possess complicated magnetic surface fields which makes their detection and in particular their modeling and reconstruction challenging. In this work we present a new Zeeman-Doppler imaging code which is especially designed for the application to late-type stars. This code uses a new multi-line cross-correlation technique by means of a principal component analysis to extract and enhance the quality of individual polarized line profiles. It implements the full polarized radiative transfer equation and uses an inversion strategy that can incorporate prior knowledge based on solar analogies. Moreover, our code utilizes a new regularization scheme which is based on local maximum entropy to allow a more appropriate reproduction of complex surface fields as those expected for late-type stars. In a first application we present Zeeman-Doppler images of II Pegasi which reveal a surprisingly large scale surface structure with one predominant (unipolar) magnetic longitude which is mainly radially oriented. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Establishing the nature of companion candidates to X-ray-emitting late B-type stars,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007S. Hubrig ABSTRACT The most favoured interpretation for the detection of X-ray emission from late B-type stars is that these stars have a yet undiscovered late-type companion (or an unbound nearby late-type star) that produces the X-rays. Several faint infrared objects at (sub)arcsecond separation from B-type stars have been uncovered in our earlier adaptive optics imaging observations, and some of them have been followed up with the high spatial resolution of the Chandra X-ray observatory, pinpointing the X-ray emitter. However, firm conclusions on their nature require a search for spectroscopic signatures of youth. Here we report on our recent ISAAC observations carried out in low-resolution spectroscopic mode. Equivalent widths have been used to obtain information on spectral types of the companions. All eight X-ray-emitting systems with late B-type primaries studied contain dwarf-like companions with spectral types later than A7. The only system in the sample where the companion turns out to be of early spectral type is not an X-ray source. These results are consistent with the assumption that the observed X-ray emission from late B-type stars is produced by an active pre-main-sequence companion star. [source] Instabilities in two-fluid magnetized media with inter-component driftMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002P. V. Tytarenko Abstract We analyse the stability of a magnetized medium consisting of a neutral fluid and a fluid of charged particles, coupled to each other through a drag force and exposed to differential body forces (for example, as the result of radiation forces on one phase). We consider a uniform equilibrium and simple model input physics, but do not arbitrarily restrict the relative orientations of the magnetic field, slip velocity and wavevector of the disturbance. We find several instabilities and classify these in terms of wave resonances. We briefly apply our results to the structure of SiO maser regions appearing in the winds from late-type stars. [source] Photometric and spectroscopic observations of three rapidly rotating late-type stars: EY Dra, V374 Peg, and GSC 02038-00293,ASTRONOMISCHE NACHRICHTEN, Issue 8 2010H. Korhonen Abstract Here, BV (RI)C broad band photometry and intermediate resolution spectroscopy in H, region are presented for two rapidly rotating late-type stars: EY Dra and V374 Peg. For a third rapid rotator, GSC 02038-00293, intermediate resolution H, spectroscopy and low resolution spectroscopy are used for spectral classification and stellar parameter investigation of this poorly known object. The low resolution spectrum of GSC 02038-00293 clearly indicates that it is a K-type star. Its intermediate resolution spectrum can be best fitted with a model with Teff = 4750 K and v sin i = 90 km s,1, indicating a very rapidly rotating mid-K star. The H, line strength is variable, indicating changing chromospheric emission on GSC 02038-00293. In the case of EY Dra and V374 Peg, the stellar activity in the photosphere is investigated from the photometric observations, and in the chromosphere from the H, line. The enhanced chromospheric emission in EY Dra correlates well with the location of the photospheric active regions, indicating that these features are spatially collocated. Hints of this behaviour are also seen in V374 Peg, but it cannot be confirmed from the current data. The photospheric activity patterns in EY Dra are stable during one observing run lasting several nights, whereas in V374 Peg large night-tonight variations are seen. Two large flares, one in the H, observations and one from the broadband photometry, and twelve smaller ones were detected in V374 Peg during the observations spanning nine nights. The energy of the photometrically detected largest flare is estimated to be 4.25 × 1031, 4.3 × 1032 erg, depending on the waveband. Comparing the activity patterns in these two stars, which are just below and above the mass limit of full convection, is crucial for understanding dynamo operation in stars with different internal structures (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Zeeman-Doppler imaging of late-type stars: The surface magnetic field of II PegASTRONOMISCHE NACHRICHTEN, Issue 10 2007T. A. Carroll Abstract Late-type stars in general possess complicated magnetic surface fields which makes their detection and in particular their modeling and reconstruction challenging. In this work we present a new Zeeman-Doppler imaging code which is especially designed for the application to late-type stars. This code uses a new multi-line cross-correlation technique by means of a principal component analysis to extract and enhance the quality of individual polarized line profiles. It implements the full polarized radiative transfer equation and uses an inversion strategy that can incorporate prior knowledge based on solar analogies. Moreover, our code utilizes a new regularization scheme which is based on local maximum entropy to allow a more appropriate reproduction of complex surface fields as those expected for late-type stars. In a first application we present Zeeman-Doppler images of II Pegasi which reveal a surprisingly large scale surface structure with one predominant (unipolar) magnetic longitude which is mainly radially oriented. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 86 GHz SiO masing late-type stars in the Inner GalaxyASTRONOMISCHE NACHRICHTEN, Issue S1 2003M. Messineo Abstract We present 86 GHz (v = 1, J = 2 , 1) SiO maser line observations with the IRAM 30-m telescope of a sample of late-type stars in the inner Galaxy (30° < l < ,30°). The stars were selected from the ISOGAL and MSX catalogues on the basis of their mid-infrared fluxes and colours. SiO maser emission was detected towards 268 (61%) of our targets, thereby doubling the number of maser line-of-sight velocities measured toward the inner Galaxy. Our sample consists mostly of Mira-like stars. They are more numerous than OH/IR stars which were previously observed to measure line-of-sight velocities. The revised longitudevelocity diagram of the inner Galaxy clearly shows a stellar nuclear disk. [source] | ||||||||||