Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpectroscopic Detection of the Pre-White Dwarf Companion of Regulus
115
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Mass transfer in an interacting binary will often strip the mass donor of its entire envelope and spin up the mass gainer to near critical rotation. The nearby B-type star Regulus represents a binary in the post-mass transfer stage: it is a rapid rotator with a very faint companion in a 40 d orbit. Here we present the results of a search for the spectral features of the stripped-down star in an extensive set of high S/N and high resolution spectra obtained with the CFHT/ESPaDOnS and TBL/NARVAL spectrographs. We first determine revised orbital elements in order to set accurate estimates of the orbital Doppler shifts at the times of observation. We then calculate cross-correlation functions of the observed and model spectra, and we search for evidence of the companion signal in the residuals after removal of the strong primary component. We detect a weak peak in the co-added residuals that has the properties expected for a faint pre-white dwarf. We use the dependence of the peak height and width on assumed secondary velocity semiamplitude to derive the semiamplitude, which yields masses of $M_1/M_odot = 3.7 pm 1.4$ and $M_2/M_odot = 0.31 pm 0.10$ (assuming orbital inclination equals the spin inclination of Regulus). We estimate the pre-white dwarf temperature $T_{rm eff} = (20 pm 4)$~kK through tests with differing temperature model spectra, and we find the radius $R_2/R_odot = 0.061 pm 0.011$ from the component temperatures and the flux ratio associated with the amplitude of the signal in the cross-correlation residuals.
rate research
Read More
We report the discovery of an extremely close, eclipsing binary system. A white dwarf is orbited by a core He-burning compact hot subdwarf star with a period as short as $simeq0.04987 {rm d}$ making this system the most compact hot subdwarf binary discovered so far. The subdwarf will start to transfer helium-rich material on short timescales of less than $50 {rm Myr}$. The ignition of He-burning at the surface may trigger carbon-burning in the core although the WD is less massive than the Chandrasekhar limit ($>0.74,M_{rm odot}$) making this binary a possible progenitor candidate for a supernova type Ia event.
We report identification of the optical counterpart to the companion of the millisecond pulsar J2317+1439. At the timing position of the pulsar, we find an object with $g=22.96pm0.05$, $r=22.86pm0.04$ and $i=22.82pm0.05$. The magnitudes and colors of the object are consistent with it being a white dwarf. By comparing with white dwarf cooling models, we estimate that it has a mass of $0.39^{+0.13}_{-0.10}$ M$_{odot}$, an effective temperature of $8077^{+550}_{-470}$ K and a cooling age of $10.9pm0.3$ Gyr. Combining our results with published constraints on the orbital parameters obtained through pulsar timing, we estimate the pulsar mass to be $3.4^{+1.4}_{-1.1}$ M$_{odot}$. Although the constraint on the pulsar mass is still weak, there is a significant possibility that the pulsar could be more massive than two solar mass.
SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity white dwarf (WD) currently known, with log g = 5.55 +/- 0.05 (M ~ 0.17 M_sun; Kilic et al. 2007a,b). Such low-mass white dwarfs (LMWDs) are believed to originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems. An optical search for J0917+4638s companion showed that it must be a compact object with a mass >= 0.28 M_sun (Kilic 2007b). Here we report on Green Bank Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to uncover a potential NS companion to the LMWD. No convincing pulsar signal is detected in our radio data. Our X-ray observation also failed to detect X-ray emission from J0917+4638s companion, while we would have detected any of the millisecond radio pulsars in 47 Tuc. We conclude that the companion is almost certainly another WD.
We present the discovery of a white dwarf companion at 3.6 from GJ3346, a nearby ($pisim$42 mas) K star observed with SPHERE@VLT as part of an open time survey for faint companions to objects with significant proper motion discrepancies ($Deltamu$) between Gaia DR1 and Tycho-2. Syrius-like systems like GJ3346AB, which include a main sequence star and a white dwarf, can be difficult to detect because of the intrinsic faintness of the latter. They have, however, been found to be common contaminants for direct imaging searches. White dwarfs have in fact similar brightness to sub-stellar companions in the infrared, while being much brighter in the visible bands like those used by Gaia. Combining our observations with Gaia DR2 and with several additional archival data sets, we were able to fully constrain the physical properties of GJ3346B, such as its effective temperature (11$times$10$^3pm$500 K) as well as the cooling age of the system (648$pm$58 Myrs). This allowed us to better understand the system history and to partially explains the discrepancies previously noted in the age indicators for this objects. Although further investigation is still needed, it seems that GJ3346, which was previously classified as young, is in fact most likely to be older than 4 Gyrs. Finally, given that the mass (0.58$pm$0.01$M_{odot}$)} and separation (85 au) of GJ3346B are compatible with the observed $Deltamu$, this discovery represents a further confirmation of the potential of this kind of dynamical signatures as selection methods for direct imaging surveys targeting faint, sub-stellar companions.
The astrometric space mission Gaia is expected to detect a large number of brown dwarf binary systems with close orbits and determine astrometric orbit solutions. This will provide key information for the formation and evolution of brown dwarfs, such as the binary frequency and dynamical masses. Known brown dwarf binaries with orbit constraints from other techniques will play an important role. We are carrying out one of the most precise and long-lasting radial velocity surveys for brown dwarf binaries in the Cha I star-forming region at the VLT. We were able to add two orbit determinations to the small group of a handful of brown dwarf and very low-mass binaries with characterized RV orbits. We show here that the astrometric motion of both systems can be detected with Gaia. We predict an astrometric signal of about 1.2 - 1.6 milliarcseconds (mas) for the brown dwarf binary ChaHa8 and of 0.4 - 0.8 mas for the very low-mass binary CHXR74. We take the luminosity of the companion into account for these estimates and present a relation for the astrometric signature of a companion with non-negligible luminosity.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
