Home About us Contact
|
Home About us Contact | ||
|
|
||
Radial Velocity Variations (radial + velocity_variation)
Selected AbstractsDiscovery of rapid radial velocity variations in the roAp star 10 Aql and possible pulsations of , CrBMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002O Kochukhov ABSTRACT We report discovery of radial velocity variations in rare earth spectral lines of the roAp star 10 Aql with amplitudes of between 30 and 130 m s,1 and periods of about 11 min. Radial velocity variations with amplitude 70 m s,1 may also have been detected in one spectral line of Fe i in , CrB. If confirmed, our results may indicate that all Ap stars in a certain temperature range pulsate, which means that roAp stars do not exist as a separate class but are only distinguished by higher pulsational amplitudes. [source] Radial velocity variations of the pulsating subdwarf B star PG 1605+072MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2002Vincent M. Woolf We present an analysis of high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Periodic radial motions are detected at frequencies similar to those reported for photometric variations in the star, with amplitudes of up to 6 km s,1. Differences between relative strengths for given frequency peaks for our velocity data and previously measured photometry are probably a result of shifting of power between modes over time. Small differences in the detected frequencies may also indicate mode-shifting. We report the detection of line-shape variations using the moments of the cross-correlation function profiles. It may be possible to use the moments to identify the pulsation modes of the star. [source] High-dispersion spectroscopy of two A supergiant systems in the Small Magellanic Cloud with novel propertiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2010R. E. Mennickent ABSTRACT We present the results of a spectroscopic investigation of two novel variable bright blue stars in the SMC, OGLE004336.91-732637.7 (SMC-SC3) and the periodically occulted star OGLE004633.76-731204.3 (SMC-SC4), whose photometric properties were reported by Mennickent et al. (2010). High-resolution spectra in the optical and far-UV show that both objects are actually A + B type binaries. Three spectra of SMC-SC4 show radial velocity variations, consistent with the photometric period of 184.26 d found in Mennickent et al. 2010. The optical spectra of the metallic lines in both systems show combined absorption and emission components that imply that they are formed in a flattened envelope. A comparison of the radial velocity variations in SMC-SC4 and the separation of the V and R emission components in the H, emission profile indicate that this envelope, and probably also the envelope around SMC-SC3, is a circumbinary disc with a characteristic orbital radius some three times the radius of the binary system. The optical spectra of SMC-SC3 and SMC-SC4 show, respectively, He i emission lines and discrete blue absorption components (BACs) in metallic lines. The high excitations of the He i lines in the SMC-SC3 spectrum and the complicated variations of Fe ii emission and absorption components with orbital phase in the spectrum of SMC-SC4 suggests that shocks occur between the winds and various static regions of the stars' corotating binary-disc complexes. We suggest that BACs arise from wind shocks from the A star impacting the circumbinary disc and a stream of former wind-efflux from the B star accreting on to the A star. The latter picture is broadly similar to mass transfer occurring in the more evolved (but less massive) algol (B/A + K) systems, except that we envision transfer occurring in the other direction and not through the inner Lagrangian point. Accordingly, we dub these objects prototype of a small group of Magellanic Cloud wind-interacting A + B binaries. [source] Post-common-envelope binaries from SDSS , I. 101 white dwarf main-sequence binaries with multiple Sloan Digital Sky Survey spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007A. Rebassa-Mansergas ABSTRACT We present a detailed analysis of 101 white dwarf main-sequence binaries (WDMS) from the Sloan Digital Sky Survey (SDSS) for which multiple SDSS spectra are available. We detect significant radial velocity variations in 18 WDMS, identifying them as post-common-envelope binaries (PCEBs) or strong PCEB candidates. Strict upper limits to the orbital periods are calculated, ranging from 0.43 to 7880 d. Given the sparse temporal sampling and relatively low spectral resolution of the SDSS spectra, our results imply a PCEB fraction of ,15 per cent among the WDMS in the SDSS data base. Using a spectral decomposition/fitting technique we determined the white dwarf effective temperatures and surface gravities, masses and secondary star spectral types for all WDMS in our sample. Two independent distance estimates are obtained from the flux-scaling factors between the WDMS spectra, and the white dwarf models and main-sequence star templates, respectively. Approximately one-third of the systems in our sample show a significant discrepancy between the two distance estimates. In the majority of discrepant cases, the distance estimate based on the secondary star is too large. A possible explanation for this behaviour is that the secondary star spectral types that we determined from the SDSS spectra are systematically too early by one to two spectral classes. This behaviour could be explained by stellar activity, if covering a significant fraction of the star by cool dark spots will raise the temperature of the interspot regions. Finally, we discuss the selection effects of the WDMS sample provided by the SDSS project. [source] Discovery of rapid radial velocity variations in the roAp star 10 Aql and possible pulsations of , CrBMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002O Kochukhov ABSTRACT We report discovery of radial velocity variations in rare earth spectral lines of the roAp star 10 Aql with amplitudes of between 30 and 130 m s,1 and periods of about 11 min. Radial velocity variations with amplitude 70 m s,1 may also have been detected in one spectral line of Fe i in , CrB. If confirmed, our results may indicate that all Ap stars in a certain temperature range pulsate, which means that roAp stars do not exist as a separate class but are only distinguished by higher pulsational amplitudes. [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] | ||||||||||