66 research outputs found
Tables of phase functions, opacities, albedos, equilibrium temperatures, and radiative accelerations of dust grains in exoplanets
There has been growing observational evidence for the presence of condensates in the atmospheres and/or comet-like tails of extrasolar planets. As a result, systematic and homogeneous tables of dust properties are useful in order to facilitate further observational and theoretical studies. In this paper we present calculations and analysis of non-isotropic phase functions, asymmetry parameter (mean cosine of the scattering angle), absorption and scattering opacities, single scattering albedos, equilibrium temperatures, and radiative accelerations of dust grains relevant for extrasolar planets. Our assumptions include spherical grain shape, Deirmendjian particle size distribution, and Mie theory. We consider several species: corundum/alumina, perovskite, olivines with 0 and 50 per cent iron content, pyroxenes with 0, 20, and 60 per cent iron content, pure iron, carbon at two different temperatures, water ice, liquid water, and ammonia. The presented tables cover the wavelength range of 0.2–500 μm and modal particle radii from 0.01 to 100 μm. Equilibrium temperatures and radiative accelerations assume irradiation by a non-blackbody source of light with temperatures from 7000 to 700 K seen at solid angles from 2π to 10−6 sr. The tables are provided to the community together with a simple code which allows for an optional, finite, angular dimension of the source of light (star) in the phase function
Revealing the Nature of Algol Disks through Optical and UV Spectroscopy, Synthetic Spectra, and Tomography of TT Hydrae
We have developed a systematic procedure to study the disks in Algol-type
binaries using spectroscopic analysis, synthetic spectra, and tomography. We
analyzed 119 H-alpha spectra of TT Hya, an Algol-type eclipsing interacting
binary, collected from 1985-2001. The new radial velocities enabled us to
derive reliable orbital elements, including a small non-zero eccentricity, and
to improve the accuracy of the absolute dimensions of the system. High
resolution IUE spectra were also analyzed to study the formation of the
ultraviolet lines and continuum. Synthetic spectra of the iron curtain using
our new shellspec program enabled us to derive a characteristic disk
temperature of 7000K. We have demonstrated that the UV emission lines seen
during total primary eclipse cannot originate from the accretion disk, but most
likely arise from a hotter disk-stream interaction region.
The synthetic spectra of the stars, disk, and stream allowed us to derive a
lower limit to the mass transfer rate of 2e-10 solar masses per year. Doppler
tomography of the observed H-alpha profiles revealed a distinct accretion disk.
The difference spectra produced by subtracting the synthetic spectra of the
stars resulted in an image of the disk, which virtually disappeared once the
composite synthetic spectra of the stars and disk were used to calculate the
difference spectra. An intensity enhancement of the resulting tomogram revealed
images of the gas stream and an emission arc. We successfully modeled the gas
stream using shellspec and associated the emission arc with an asymmetry in the
accretion disk.Comment: 46 pages, 15 figures, 6 tables, accepted by Ap
Diagnosing the Clumpy Protoplanetary Disk of the UXor Type Young Star GM Cephei
UX Orionis stars (UXors) are Herbig Ae/Be or T Tauri stars exhibiting
sporadic occultation of stellar light by circumstellar dust. GM\,Cephei is such
a UXor in the young (~Myr) open cluster Trumpler\,37, showing prominent
infrared excess, emission-line spectra, and flare activity. Our photometric
monitoring (2008--2018) detects (1)~an 3.43~day period, likely arising
from rotational modulation by surface starspots, (2)~sporadic brightening on
time scales of days due to accretion, (3)~irregular minor flux drops due to
circumstellar dust extinction, and (4)~major flux drops, each lasting for a
couple of months with a recurrence time, though not exactly periodic, of about
two years. The star experiences normal reddening by large grains, i.e., redder
when dimmer, but exhibits an unusual "blueing" phenomenon in that the star
turns blue near brightness minima. The maximum extinction during relatively
short (lasting ~days) events, is proportional to the duration, a
consequence of varying clump sizes. For longer events, the extinction is
independent of duration, suggestive of a transverse string distribution of
clumps. Polarization monitoring indicates an optical polarization varying
--8, with the level anticorrelated with the slow brightness
change. Temporal variation of the unpolarized and polarized light sets
constraints on the size and orbital distance of the circumstellar clumps in the
interplay with the young star and scattering envelope. These transiting clumps
are edge-on manifestations of the ring- or spiral-like structures found
recently in young stars with imaging in infrared of scattered light, or in
submillimeter of thermalized dust emission.Comment: 20 pages, 9 figure
Looking into the cradle of the grave : J22564–5910, a potential young post-merger hot subdwarf
Context. We present the discovery of J22564–5910, a new type of hot subdwarf (sdB) which shows evidence of gas present in the system and it has shallow, multi-peaked hydrogen and helium lines which vary in shape over time. All observational evidence points towards J22564–5910 being observed very shortly after the merger phase that formed it.
Aims. Using high-resolution, high signal-to-noise spectroscopy, combined with multi-band photometry, Gaia astrometry, and TESS light curves, we aim to interpret these unusual spectral features.
Methods. The photometry, spectra, and light curves were all analysed, and their results were combined in order to support our interpretation of the observations: the likely presence of a magnetic field combined with gas features around the sdB. Based on the triple-peaked H lines, the magnetic field strength was estimated and, by using the SHELLSPEC code, qualitative models of gas configurations were fitted to the observations.
Results. All observations can either be explained by a magnetic field of ∼650 kG, which enables the formation of a centrifugal magnetosphere, or a non-magnetic hot subdwarf surrounded by a circumstellar gas disc or torus. Both scenarios are not mutually exclusive and both can be explained by a recent merger.
Conclusions. J22564–5910 is the first object of its kind. It is a rapidly spinning sdB with gas still present in the system. It is the first post-merger star observed this early after the merger event, and as such it is very valuable system to test merger theories. If the magnetic field can be confirmed, it is not only the first magnetic sdB, but it hosts the strongest magnetic field ever found in a pre-white dwarf object. Thus, it could represent the long sought-after immediate ancestor of strongly magnetic white dwarfs
Impact of Diabetes Mellitus and Chronic Kidney Disease on Cardiovascular Outcomes and Platelet P2Y(12) Receptor Antagonist Effects in Patients With Acute Coronary Syndromes : Insights From the PLATO Trial
Background-There are limited data on how the combination of diabetes mellitus (DM) and chronic kidney disease (CKD) affects cardiovascular outcomes as well as response to different P2Y(12) receptor antagonists, which represented the aim of the present investigation. Methods and Results-In this post hoc analysis of the PLATO (Platelet Inhibition and Patient Outcomes) trial, which randomized acute coronary syndrome patients to ticagrelor versus clopidogrel, patients (n=15 108) with available DM and CKD status were classified into 4 groups: DM+/CKD+ (n=1058), DM+/CKD- (n=2748), DM-/CKD+ (n=2160), and DM-/CKD- (n=9142). The primary efficacy end point was a composite of cardiovascular death, myocardial infarction, or stroke at 12 months. The primary safety end point was PLATO major bleeding. DM+/CKD+ patients had a higher incidence of the primary end point compared with DM-/CKD- patients (23.3% versus 7.1%; adjusted hazard ratio 2.22; 95% CI 1.88-2.63; P Conclusions-In acute coronary syndrome patients, a gradient of risk was observed according to the presence or absence of DM and CKD, with patients having both risk factors at the highest risk. Although the ischemic benefit of ticagrelor over clopidogrel was consistent in all subgroups, the absolute risk reduction was greatest in patients with both DM and CKD.Peer reviewe
Short-period Kepler exoplanet candidates: Search for a circum-planetary material
This article deals with a sample of 20 shortperiod exoplanet candidates with a period similar to KIC012557548b from the Kepler mission. KIC012557548b is an exoplanet candidate which shows a variable and asymmetric transit. It is most probably due to a comet-like tail emerging from the exoplanet. Our main aim is to search for comet-like tails similar to KIC012557548b, or another form of circum-planetary material
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