Three dimensional Doppler tomography Marsh, T R
Monthly notices of the Royal Astronomical Society,
02/2022, Letnik:
510, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Doppler tomography is a method to compute the emissivity distribution within the co-rotating frames of binary stars from observations of their emission line profiles at multiple orbital ...phases. A key assumption of the method as it is usually applied is that all gas flow is parallel to the orbital plane of the binary. In this paper, I examine the possibility of lifting this assumption to allow for motion parallel to the orbital ‘z’ axis of the binary as well. I show that the problem is best considered in Fourier space, and that line profiles directly constrain the 3D Fourier transform of the 3D Doppler image in velocity space, but only over the 2D surface of a double-cone centred upon the origin, and aligned with the axis reciprocal to the vz velocity axis. Hence the full information needed for the recovery of the 3D emissivity distribution is simply not available. Despite this, an inversion method is presented and tested on a number of simulated images. While artefacts resulting from the missing information do appear, the tests suggest that there could be some value in applying 3D Doppler tomography to data from real systems, although considerable care is needed when doing so.
The scatter of the M dwarf mass–radius relationship Parsons, S G; Gänsicke, B T; Marsh, T R ...
Monthly Notices of the Royal Astronomical Society,
11/2018, Letnik:
481, Številka:
1
Journal Article, Publication
Recenzirano
Odprti dostop
M dwarfs are prime targets in the hunt for habitable worlds around other stars. This
is due to their abundance as well as their small radii and low masses and tempera-
tures, which facilitate the ...detection of temperate, rocky planets in orbit around them.
However, the fundamental properties of M dwarfs are difficult to constrain, often lim-
iting our ability to characterise the planets they host. Here we test several theoretical
relationships for M dwarfs by measuring 23 high precision, model-independent masses
and radii for M dwarfs in binaries with white dwarfs. We find a large scatter in the
radii of these low-mass stars, with 25 per cent having radii consistent with theoret-
ical models while the rest are up to 12 per cent over-inflated. This scatter is seen
in both partially- and fully-convective M dwarfs. No clear trend is seen between the
over-inflation and age or metallicity, but there are indications that the radii of slowly
rotating M dwarfs are more consistent with predictions, albeit with a similar amount of
scatter in the measurements compared to more rapidly rotating M dwarfs. The sample
of M dwarfs in close binaries with white dwarfs appears indistinguishable from other
M dwarf samples, implying that common envelope evolution has a negligible impact on
their structure. We conclude that theoretical and empirical mass-radius relationships
lack the precision and accuracy required to measure the fundamental parameters of
M dwarfs well enough to determine the internal structure and bulk composition of the
planets they host.
Peer Reviewed
The Ribosomal Database Project (RDP) provides researchers with quality-controlled bacterial and archaeal small subunit rRNA alignments and analysis tools. An improved alignment strategy uses the ...Infernal secondary structure aware aligner to provide a more consistent higher quality alignment and faster processing of user sequences. Substantial new analysis features include a new Pyrosequencing Pipeline that provides tools to support analysis of ultra high-throughput rRNA sequencing data. This pipeline offers a collection of tools that automate the data processing and simplify the computationally intensive analysis of large sequencing libraries. In addition, a new Taxomatic visualization tool allows rapid visualization of taxonomic inconsistencies and suggests corrections, and a new class Assignment Generator provides instructors with a lesson plan and individualized teaching materials. Details about RDP data and analytical functions can be found at http://rdp.cme.msu.edu/.
Abstract
We present a search for optical bursts from the repeating fast radio burst FRB 121102 using simultaneous observations with the high-speed optical camera ULTRASPEC on the 2.4-m Thai National ...Telescope and radio observations with the 100-m Effelsberg Radio Telescope. A total of 13 radio bursts were detected, but we found no evidence for corresponding optical bursts in our 70.7-ms frames. The 5σ upper limit to the optical flux density during our observations is 0.33 mJy at 767 nm. This gives an upper limit for the optical burst fluence of 0.046 Jy ms, which constrains the broad-band spectral index of the burst emission to α ≤ −0.2. Two of the radio pulses are separated by just 34 ms, which may represent an upper limit on a possible underlying periodicity (a rotation period typical of pulsars), or these pulses may have come from a single emission window that is a small fraction of a possible period.
Whether or not climate change has had an impact on the occurrence of tornadoes in the United States has become a question of high public and scientific interest, but changes in how tornadoes are ...reported have made it difficult to answer it convincingly. We show that, excluding the weakest tornadoes, the mean annual number of tornadoes has remained relatively constant, but their variability of occurrence has increased since the 1970s. This is due to a decrease in the number of days per year with tornadoes combined with an increase in days with many tornadoes, leading to greater variability on annual and monthly time scales and changes in the timing of the start of the tornado season.
Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large ...radial velocity survey for double degenerate (DD) binaries using the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY – SPY). Exposures taken at different epochs are checked for radial velocity shifts indicating close binary systems. We observed 689 targets classified as DA white dwarfs (displaying hydrogen-rich atmospheres), of which 46 were found to possess a cool companion. We measured radial velocities (RV) of the remaining 643 DA white dwarfs. We managed to secure observations at two or more epochs for 625 targets, supplemented by eleven objects meeting our selection criteria from literature. The data reduction and analysis methods applied to the survey data are described in detail. The sample contains 39 double degenerate binaries, only four of which were previously known. Twenty are double-lined systems, in which features from both components are visible, the other 19 are single-lined binaries. We provide absolute RVs transformed to the heliocentric system suitable for kinematic studies. Our sample is large enough to sub-divide by mass: 16 out of 44 low mass targets (≤0.45 M⊙) are detected as DDs, while just 23 of the remaining 567 targets with multiple spectra and mass > 0.45 M⊙ are double. The detected fraction amongst the low mass objects (36.4 ± 7.3%) is significantly higher than for the higher-mass, carbon-oxygen core dominated part of the sample (3.9 ± 0.8%), but it is much lower than expected from the detection efficiency for companion masses of 0.05 M⊙ or higher and a 100% binary fraction. This suggests either companion stars of with a mass below 0.05 M⊙ or some of the low mass white dwarfs are single.
Context.
The distribution of the specific intensity over the stellar disk is an essential tool for modeling the light curves in eclipsing binaries, planetary transits, and stellar diameters through ...interferometric techniques, line profiles in rotating stars, gravitational microlensing, etc. However, the available theoretical calculations are mostly restricted to stars on the main sequence or the giant branch, and very few calculations are available for compact stars.
Aims.
The main objective of the present work is to extend these investigations by computing the gravity and limb-darkening coefficients for white dwarf atmosphere models with hydrogen, helium, or mixed compositions (types DA, DB, and DBA).
Methods.
We computed gravity and limb-darkening coefficients for DA, DB, and DBA white dwarfs atmosphere models, covering the transmission curves of the Sloan, UBVRI,
Kepler
, TESS, and
Gaia
photometric systems. Specific calculations for the HiPERCAM instrument were also carried out. For all calculations of the limb-darkening coefficients we used the least-squares method. Concerning the effects of tidal and rotational distortions, we also computed for the first time the gravity-darkening coefficients
y
(
λ
) for white dwarfs using the same models of stellar atmospheres as in the case of limb-darkening. A more general differential equation was introduced to derive these quantities, including the partial derivative (
∂
ln
I
o
(
λ
)/
∂
ln
g
)
T
eff
.
Results.
Six laws were adopted to describe the specific intensity distribution: linear, quadratic, square root, logarithmic, power-2, and a more general one with four coefficients. The computations are presented for the chemical compositions logH/He = −10.0 (DB), −2.0 (DBA) and He/H = 0 (DA), with log
g
varying between 5.0 and 9.5 and effective temperatures between 3750 and 100 000 K. For effective temperatures higher than 40 000 K, the models were also computed adopting nonlocal thermal equilibirum (DA). The adopted mixing-length parameters are ML2/
α
= 0.8 (DA case) and 1.25 (DB and DBA). The results are presented in the form of 112 tables. Additional calculations, such as for other photometric systems and/or different values of logH/He, log
g
, and
T
eff
can be performed upon request.
Gaseous Metal Disk Around a White Dwarf Gänsicke, B.T; Marsh, T.R; Southworth, J ...
Science (American Association for the Advancement of Science),
12/2006, Letnik:
314, Številka:
5807
Journal Article
Recenzirano
The destiny of planetary systems through the late evolution of their host stars is very uncertain. We report a metal-rich gas disk around a moderately hot and young white dwarf. A dynamical model of ...the double-peaked emission lines constrains the outer disk radius to just 1.2 solar radii. The likely origin of the disk is a tidally disrupted asteroid, which has been destabilized from its initial orbit at a distance of more than 1000 solar radii by the interaction with a relatively massive planetesimal object or a planet. The white dwarf mass of 0.77 solar mass implies that planetary systems may form around high-mass stars.
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