Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSDSS J0349-0059 is a GW Virginis star
85
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
High speed photometric observations of the spectroscopically-discovered PG 1159 star SDSS J034917.41-005917.9 in 2007 and 2009 reveal a suite of pulsation frequencies in the range of 1038 - 3323 microHz with amplitudes between 3.5 and 18.6 mmag. SDSS J034917.41-005917.9 is therefore a member of the GW Vir class of pulsating pre-white dwarfs. We have identified 10 independent pulsation frequencies that can be fitted by an asymptotic model with a constant period spacing of 23.61 +/- 0.21 s, presumably associated with a sequence of l = 1 modes. The highest amplitude peak in the suite of frequencies shows evidence for a triplet structure, with a frequency separation of 14.4 microHz. Five of the identified frequencies do not fit the l = 1 sequence, but are, however, well-modeled by an independent asymptotic sequence with a constant period spacing of 11.66 +/- 0.13 s. It is unclear to which l mode these frequencies belong.
rate research
Read More
The Gaia Data Release 2 provides a parallax of 0.734+/-0.073 mas for SDSS J102915+172927, currently the most metal-poor known object. This parallax implies that it is dwarf star, ruling out the scenario that it is a subgiant. The subgiant scenario had as a corollary that the star had been formed in a medium highly enriched in C, thus making line cooling efficient during the collapse, that was also highly enriched in Fe by Type Ia SNe. This scenario can also now be ruled out for this star, reinforcing the need of dust cooling and fragmentation to explain its formation.
A growing number of eclipsing binary systems of the HW Vir kind (i. e., composed by a subdwarf-B/O primary star and an M dwarf secondary) show variations in their orbital period, also called Eclipse Time Variations (ETVs). Their physical origin is not yet known with certainty: while some ETVs have been claimed to arise from dynamical perturbations due to the presence of circumbinary planetary companions, other authors suggest that the Applegate effect or other unknown stellar mechanisms could be responsible for them. In this work, we present twenty-eight unpublished high-precision light curves of one of the most controversial of these systems, the prototype HW Virginis. We homogeneously analysed the new eclipse timings together with historical data obtained between 1983 and 2012, demonstrating that the planetary models previously claimed do not fit the new photometric data, besides being dynamically unstable. In an effort to find a new model able to fit all the available data, we developed a new approach based on a global-search genetic algorithm and eventually found two new distinct families of solutions that fit the observed timings very well, yet dynamically unstable at the 10^5-year time scale. This serves as a cautionary tale on the existence of formal solutions that apparently explain ETVs but are not physically meaningful, and on the need of carefully testing their stability. On the other hand, our data confirm the presence of an ETV on HW Vir that known stellar mechanisms are unable to explain, pushing towards further observing and modelling efforts.
The late-B magnetic chemically peculiar star CU Vir is one of the fastest rotators among the intermediate-mass stars with strong fossil magnetic fields. It shows a prominent rotational modulation of the spectral energy distribution and absorption line profiles due to chemical spots and exhibits a unique strongly beamed variable radio emission. Little is known about the magnetic field topology of CU Vir. In this study we aim to derive, for the first time, detailed maps of the magnetic field distribution over the surface of this star. We use high-resolution spectropolarimetric observations covering the entire rotational period. These data are interpreted using a multi-line technique of least-squares deconvolution (LSD) and a new Zeeman Doppler imaging code based on detailed polarised radiative transfer modelling of the Stokes I and V LSD profiles. This new magnetic inversion approach relies on the spectrum synthesis calculations over the full wavelength range covered by observations and does not assume that the LSD profiles behave as a single spectral line with mean parameters. We present magnetic and chemical abundance maps derived from the Si and Fe lines. Mean polarisation profiles of both elements reveal a significant departure of the magnetic field topology of CU Vir from the commonly assumed axisymmetric dipolar configuration. The field of CU Vir is dipolar-like, but clearly non-axisymmetric, showing a large difference of the field strength between the regions of opposite polarity. The main relative abundance depletion features in both Si and Fe maps coincide with the weak-field region in the magnetic map. Detailed information on the distorted dipolar magnetic field topology of CU Vir provided by our study is essential for understanding chemical spot formation, radio emission, and rotational period variation of this star.
Context: The Mira variable LX Cyg showed a dramatic increase of its pulsation period in the recent decades and appears to undergo an important transition in its evolution. Aims: We aim at investigating the spectral type evolution of this star over the recent decades as well as during one pulsation cycle in more detail and discuss it in connection with the period evolution. Methods: We present optical, near- and mid-IR low-resolution as well as optical high-resolution spectra to determine the current spectral type. The optical spectrum of LX Cyg has been followed for more than one pulsation cycle. Recent spectra are compared to archival spectra to trace the spectral type evolution and a Spitzer mid-IR spectrum is analysed for the presence of molecular and dust features. Furthermore, the current period is derived from AAVSO data. Results: It is found that the spectral type of LX Cyg changed from S to C sometime between 1975 and 2008. Currently, the spectral type C is stable during a pulsation cycle. It is shown that spectral features typical of C-type stars are present in its spectrum from ~0.5 to 14 $mu{rm{m}}$. An emission feature at 10.7 $mu{rm{m}}$ is attributed to SiC grains. The period of LX Cyg has increased from ~460 d to ~580 d within only 20 years, and is stable now. Conclusions: We conclude that the change in spectral type and the increase in pulsation period happened simultaneously and are causally connected. Both a recent thermal pulse (TP) and a simple surface temperature decrease appear unlikely to explain the observations. We therefore suggest that the underlying mechanism is related to a recent third dredge-up mixing event that brought up carbon from the interior of the star, i.e. that a genuine abundance change happened. We propose that LX Cyg is a rare transition type object that is uniquely suited to study the transformation from O- to C-rich stars in detail.
LAMOST J202629.80+423652.0 has been recently classified as a new symbiotic star containing a long-period Mira, surrounded by dust (D-type) and displaying in the optical spectra high ionization emission lines, including the Raman-scattered OVI at 6825 Ang. We have observed LAMOST J202629.80+423652.0 photometrically in the BVRI bands and spectroscopically over the 3500-8000 Ang range. We have found it to be a normal G8IV sub-giant star, deprived of any emission line in its spectrum, and reddened by E(B-V)=0.35 mag. Combining our photometry with data from all-sky patrol surveys, we find LAMOST J202629.80+423652.0 to be non variable, so not pulsating as a Mira. We have compiled from existing sources its spectral energy distribution, extending well into the mid-Infrared, and found it completely dominated by the G8IV photospheric stellar emission, without any sign of circumstellar dust. We therefore conclude that LAMOST J202629.80+423652.0 is not a symbiotic star, nor it is pulsating or been enshrouded in dust.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
