Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpectral and spatial imaging of the Be+sdO binary phi Persei
111
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The rapidly rotating Be star phi Persei was spun up by mass and angular momentum transfer from a now stripped-down, hot subdwarf companion. Here we present the first high angular resolution images of phi Persei made possible by new capabilities in longbaseline interferometry at near-IR and visible wavelengths. We observed phi Persei with the MIRC and VEGA instruments of the CHARA Array. Additional MIRC-only observations were performed to track the orbital motion of the companion, and these were fit together with new and existing radial velocity measurements of both stars to derive the complete orbital elements and distance. The hot subdwarf companion is clearly detected in the near-IR data at each epoch of observation with a flux contribution of 1.5% in the H band, and restricted fits indicate that its flux contribution rises to 3.3% in the visible. A new binary orbital solution is determined by combining the astrometric and radial velocity measurements. The derived stellar masses are 9.6+-0.3Msol and 1.2+-0.2Msol for the Be primary and subdwarf secondary, respectively. The inferred distance (186 +- 3 pc), kinematical properties, and evolutionary state are consistent with membership of phi Persei in the alpha Per cluster. From the cluster age we deduce significant constraints on the initial masses and evolutionary mass transfer processes that transformed the phi Persei binary system. The interferometric data place strong constraints on the Be disk elongation, orientation, and kinematics, and the disk angular momentum vector is coaligned with and has the same sense of rotation as the orbital angular momentum vector. The VEGA visible continuum data indicate an elongated shape for the Be star itself, due to the combined effects of rapid rotation, partial obscuration of the photosphere by the circumstellar disk, and flux from the bright inner disk.
rate research
Read More
Stripped-envelope stars (SESs) form in binary systems after losing mass through Roche-lobe overflow. They bear astrophysical significance as sources of UV and ionizing radiation in older stellar populations and, if sufficiently massive, as stripped supernova progenitors. Binary evolutionary models predict them to be common, but only a handful of subdwarfs (i.e., SESs) with B-type companions are known. This could be the result of observational biases hindering detection, or an incorrect understanding of binary evolution. We reanalyze the well-studied post-interaction binary phi Persei. Recently, new data improved the orbital solution of the system, which contains a ~1.2 Msun SES and a rapidly rotating ~9.6 Msun Be star. We compare with an extensive grid of evolutionary models using a Bayesian approach and find initial masses of the progenitor of 7.2+/-0.4 Msun for the SES and 3.8+/-0.4 Msun for the Be star. The system must have evolved through near-conservative mass transfer. These findings are consistent with earlier studies. The age we obtain, 57+/-9 Myr, is in excellent agreement with the age of the alpha Persei cluster. We note that neither star was initially massive enough to produce a core-collapse supernova, but mass exchange pushed the Be star above the mass threshold. We find that the subdwarf is overluminous for its mass by almost an order of magnitude, compared to the expectations for a helium core burning star. We can only reconcile this if the subdwarf is in a late phase of helium shell burning, which lasts only 2-3% of the total lifetime as a subdwarf. This could imply that up to ~50 less evolved, dimmer subdwarfs exist for each system similar to phi Persei. Our findings can be interpreted as a strong indication that a substantial population of SESs indeed exists, but has so far evaded detection because of observational biases and lack of large-scale systematic searches.
We present spectroscopic observations of the Be/X-ray binary X Per obtained during the period December 2017 - January 2020 (MJD~58095 - MJD~58865). In December 2017 the $Halpha$, $Hbeta$, and HeI 6678 emission lines were symmetric with violet-to-red peak ratio $V/R approx 1$. During the first part of the period (December 2017 - August 2018) the V/R-ratio decreased to 0.5 and the asymmetry developed simultaneously in all three lines. In September 2018, a third component with velocity $approx 250$~km~s$^{-1}$ appeared on the red side of the HeI line profile. Later this component emerged in $Hbeta$, accompanied by the appearance of a red shoulder in $Halpha$. Assuming that it is due to an eccentric wave in the circumstellar disc, we find that the eccentric wave appeared first in the innermost part of the disc, it spreads out with outflowing velocity $v_{wave} approx 1.1 pm 0.2 $~km~s$^{-1}$, and the eccentricity of the eccentric wave is $e_{wave} approx 0.29 pm 0.07$. A detailed understanding of the origin of such eccentricities would have applications to a wide range of systems from planetary rings to AGNs.
Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed IR-excess and emission lines. The influence of binarity on these phenomena remains controversial. delta Sco is a binary system whose primary suddently began to exhibit the Be phenomenon at the last periastron in 2000. We want to constrain the geometry and kinematics of its circumstellar environment. We observed the star between 2007 and 2010 using spectrally-resolved interferometry with the VLTI/AMBER and CHARA/VEGA instruments. We found orbital elements that are compatible with previous estimates. The next periastron should take place around July 5, 2011 (+- 4,days). We resolved the circumstellar disk in the HAlpha (FWHM = 4.8+-1.5mas), BrGamma (FWHM = 2.9 0.,mas), and the 2.06$ mu$m HeI (FWHM = 2.4+-0.3mas) lines as well as in the K band continuum (FWHM ~2.4mas). The disk kinematics are dominated by the rotation, with a disk expansion velocity on the order of 0.2km/s. The rotation law within the disk is compatible with Keplerian rotation. As the star probably rotates at about 70% of its critical velocity the ejection of matter doesnt seems to be dominated by rotation. However, the disk geometry and kinematics are similar to that of the previously studied quasi-critically rotating Be stars, namely Alpha Ara, Psi Per and 48 Per.
Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed infrared (IR) excess and emission lines. The influence of binarity on these phenomena remains controversial. We followed the evolution of the environment surrounding the binary Be star $delta$ Scorpii one year before and one year after the 2011 periastron to check for any evidence of a strong interaction between its companion and the primary circumstellar disk. We used the VLTI/AMBER spectro-interferometric instrument operating in the K band in high (12000) spectral resolution to obtain information on both the disk geometry and kinematics. Observations were carried out in two emission lines: Br$gamma$ (2.172,$mu$m) and $ion{He}{i}$ (2.056,$mu$m). We detected some important changes in $delta$ Scorpiis circumstellar disk geometry between the first observation made in April 2010 and the new observation made in June 2012. During the last two years the disk has grown at a mean velocity of 0.2,km,s$^{-1}$. This is compatible with the expansion velocity previously found during the 2001-2007 period. The disk was also found to be asymmetric at both epochs, but with a different morphology in 2010 and 2012. Considering the available spectroscopic data showing that the main changes in the emission-line profiles occurred quickly during the periastron, it is probable that the differences between the 2010 and 2012 disk geometry seen in our interferometric data stem from a disk perturbation caused by the companion tidal effects. However, taking into account that no significant changes have occurred in the disk since the end of the 2011 observing season, it is difficult to understand how this induced inhomogeneity has been frozen in the disk for such a long period.
We present blue optical spectra of 92 members of h and chi Per obtained with the WIYN telescope at Kitt Peak National Observatory. From these spectra, several stellar parameters were measured for the B-type stars, including V sin i, T_eff, log g_polar, M_star, and R_star. Stromgren photometry was used to measure T_eff and log g_polar for the Be stars. We also analyze photometric data of cluster members and discuss the near-to-mid IR excesses of Be stars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
