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V Sin (v + sin)
Selected AbstractsRotational velocities of the giants in symbiotic stars , III.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Evidence of fast rotation in S-type symbiotics ABSTRACT We have measured the projected rotational velocities (v sin i) in a number of symbiotic stars and M giants using high-resolution spectroscopic observations. On the basis of our measurements and data from the literature, we compare the rotation of mass donors in symbiotics with v sin i of field giants and find that: (i) the K giants in S-type symbiotics rotate at v sin i > 4.5 km s,1, which is 2,4 times faster than the field K giants; (ii) the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. Statistical tests show that these differences are highly significant , p-value <10,3 in the spectral-type bins K2III-K5III, M0III-M6III and M2III-M5III and (iii) our new observations of D'-type symbiotics also confirm that they are fast rotators. As a result of the rapid rotation, the cool giants in symbiotics should have 3,30 times larger mass-loss rates. Our results suggest also that bipolar ejections in symbiotics seem to happen in objects where the mass donors rotate faster than the orbital period. All spectra used in our series of papers can be obtained upon request from the authors. [source] H, long-term monitoring of the Be star , Cephei AaMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008G. Catanzaro ABSTRACT Papers published in recent years have contributed to resolve the enigma of the hypothetical Be nature of the hot pulsating star , Cephei. This star shows variable emission in the H, line, typical for Be stars, but its projected rotational velocity is very much lower than the critical limit, contrary to what is expected for a typical Be star. The emission has been attributed to the secondary component of the , Cephei spectroscopic binary system. In this paper, using both our and archived spectra, we attempt to recover the H, profile of the secondary component and to analyse its behaviour with time for a long period. To accomplish this task, we first derive the atmospheric parameters of the primary, Teff= 24 000 ± 250 K and log g= 3.91 ± 0.10, and then we use these values to compute its synthetic H, profile, and finally we reconstruct the secondary's profile disentangling the observed one. The secondary's H, profile shows the typical two-peak emission of a Be star with a strong variability. We also analysed the behaviour versus time of some linewidth parameters: equivalent width, ratio of blue to red peak intensities, full width at half-maximum, peak separation and radial velocity of the central depression. The projected rotational velocity (v sin i) of the secondary and the dimension of the equatorial surrounding disc have also been estimated. [source] Surface abundances of light elements for a large sample of early B-type stars , III.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004An analysis of helium lines in spectra of 102 stars ABSTRACT Non-local thermodynamic equilibrium analysis of He i lines in spectra of 102 B stars is implemented in order to derive the helium abundance He/H, the microturbulent parameter Vt and the projected rotation velocity v sin i. A simultaneous determination of He/H and Vt for the stars is effected by analysing equivalent widths of the 4471- and 4922-Å lines primarily as indicators of He/H and the 4713-, 5016-, 5876- and 6678-Å lines primarily as indicators of Vt. The rotation velocities v sin i are found from profiles of the same lines. It is shown that, when Vt > 7 km s,1, the Vt(He i) values determined from He i lines are systematically overestimated as compared with the Vt(O ii, N ii) values derived from O ii and N ii lines. This discrepancy is especially appreciable for hot evolved B giants with Vt(He i) = 16,23 km s,1 and may indicate a failure of classical model atmospheres to represent the strong He i lines for these stars. Two programme stars, HR 1512 and 7651, are found to be helium-weak stars. The remaining 100 stars are divided into three groups according to their masses M. The microturbulent parameter Vt(He i) is low for all stars of group A (M= 4.1,6.9 M,) and for all stars with the relative ages t/tMS < 0.8 of group B (M= 7.0,11.2 M,). Their Vt(He i) values are within the 0 to 5 km s,1 range, as a rule; the mean value is Vt= 1.7 km s,1. Only evolved giants of group B, which are close to the termination of the main-sequence (MS) evolutionary phase (t/tMS > 0.8), show Vt(He i) up to 11 km s,1. The helium abundance He/H is correlated with the relative age t/tMS in both groups; the averaged He/H enhancement during the MS phase is 26 per cent. For group C, containing the most massive stars (M= 12.4,18.8 M,), the Vt(He i) values display a correlation with t/tMS, varying from 4 to 23 km s,1. The He/H determination for hot evolved B giants of the group with Vt(He i) > 15 km s,1 depends on a choice between the Vt(He i) and Vt(O ii, N ii) scales. The mean He/H enrichment by 67 per cent during the MS phase is found, if the abundances He/H are based on the Vt(O ii, N ii) scale; however, two evolved giants with especially high v sin i, HR 7446 and 7993, show the He/H enhancement by about a factor of 2.5. When using the same Vt scale, we found a trend of He/H with projected rotational velocities v sin i; a large dispersion for v sin i > 150 km s,1 can result from differences in masses M. A comparison with the stellar model computations with rotationally induced mixing shows that the observed helium enrichment during the MS phase can be explained by rotation with initial velocities 250,400 km s,1. The He/H distribution on M and v sin i based on the Vt(O ii, N ii) scale seems to be in better agreement with the theory than one based on the Vt(He i) scale. The mean value He/H = 0.10 derived for stars in the zero age main sequence (ZAMS) vicinity can be adopted as the typical initial helium abundance for early B stars in the solar neighbourhood. [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] HD 1: The number-one star in the sky,ASTRONOMISCHE NACHRICHTEN, Issue 4 2010K.G. Strassmeier Abstract We present the first ever study of the bright star HD 1. The star was chosen arbitrarily just because of its outstanding Henry Draper number. Surprisingly, almost nothing is known about this bright 7.m4 star. Our observations were performed as part of the commissioning of the robotic telescope facility STELLA and its fiber-fed high-resolution optical echelle spectrograph SES in the years 2007,2010. We found long-term radial velocity variations with a full amplitude of 9 km s,1 with an average velocity of ,29.8 km s,1 and suggest the star to be a hitherto unknown single-lined spectroscopic binary. A preliminary orbit with a period of 6.2 years (2279±69 days) and an eccentricity of 0.50±0.01 is given. Its rms uncertainty is just 73 m s,1. HD 1 appears to be a G9-K0 giant of luminosity class IIIa with Teff = 4850±100 K, logg = 2.0±0.2, L , 155 L,, a mass of 3.0±0.3 M,, a radius of 17.7 R,, and an age of ,350 Myr. A relative abundance analysis led to a metallicity of [Fe/H] = ,0.12 ± 0.09. The , -element silicon may indicate an overabundance of +0.13 though. The low strengths of some s-process lines and a lower limit for the 12C/13C isotope ratio of ,16 indicate that HD 1 is on the first ascend of the RGB. The absorption spectral lines appear rotationally broadened with a v sin i of 5.5±1.2 km s,1 but no chromospheric activity is evident. We also present photometric monitoring BV (RI)C data taken in parallel with STELLA. The star is likely a small-amplitude (<10 mmag) photometric variable although no periodicity was found (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Orbital eccentricity of the symbiotic star MWC 560,ASTRONOMISCHE NACHRICHTEN, Issue 3 2010R.K. Zamanov Abstract We present projected rotational velocity measurements of the red giant in the symbiotic star MWC 560, using the high-resolution spectroscopic observations with the FEROS spectrograph. We find that the projected rotational velocity of the red giant is v sin i = 8.2 ± 1.5 km s,1, and estimate its rotational period tobe Prot = 144,306 days. Using the theoretical predictions of tidal interaction and pseudosynchronization, we estimate the orbital eccentricity e = 0.68,0.82. We briefly discuss the connection of our results with the photometric variability of the object (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New magnetic field measurements of , Cephei stars and slowly pulsating B stars,ASTRONOMISCHE NACHRICHTEN, Issue 4 2009S. Hubrig Abstract We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B-type stars consisting of confirmed or candidate , Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B-type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three , Cephei stars and two stars suspected to be , Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3, has been diagnosed in two normal B-type stars, the nitrogen-rich early B-type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of , Cephei stars have detected magnetic fields: Out of 13 , Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected , Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non-magnetic pulsating stars in the H-R diagram. We find that their domains in the H-R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i -values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||