8 research outputs found
Intriguing X-ray and optical variations of the gamma Cas analog HD45314
A growing number of Be and Oe stars, named the gamma Cas stars, are known for
their unusually hard and intense X-ray emission. This emission could either
trace accretion by a compact companion or magnetic interaction between the star
and its decretion disk. To test these scenarios, we carried out a detailed
optical monitoring of HD45314, the hottest member of the class of gamma Cas
stars, along with dedicated X-ray observations on specific dates.
High-resolution optical spectra were taken to monitor the emission lines formed
in the disk, while X-ray spectroscopy was obtained at epochs when the optical
spectrum of the Oe star was displaying peculiar properties. Over the last four
years, HD45314 has entered a phase of spectacular variations. The optical
emission lines have undergone important morphology and intensity changes
including transitions between single- and multiple-peaked emission lines as
well as shell events, and phases of (partial) disk dissipation. Photometric
variations are found to be anti-correlated with the equivalent width of the
H-alpha emission. Whilst the star preserved its hard and bright X-ray emission
during the shell phase, the X-ray spectrum during the phase of (partial) disk
dissipation was significantly softer and weaker. The observed behaviour of
HD45314 suggests a direct association between the level of X-ray emission and
the amount of material simultaneously present in the Oe disk as expected in the
magnetic star-disk interaction scenario.Comment: Accepted for publication in A&
The orbit and stellar masses of the archetype colliding-wind binary WR 140
We present updated orbital elements for the Wolf-Rayet (WR) binary WR 140 (HD
193793; WC7pd + O5.5fc). The new orbital elements were derived using previously
published measurements along with 160 new radial velocity measurements across
the 2016 periastron passage of WR 140. Additionally, four new measurements of
the orbital astrometry were collected with the CHARA Array. With these
measurements, we derive stellar masses of
and . We also include a discussion of the
evolutionary history of this system from the Binary Population and Spectral
Synthesis (BPASS) model grid to show that this WR star likely formed primarily
through mass loss in the stellar winds, with only a moderate amount of mass
lost or transferred through binary interactions.Comment: 10 pages, 5 figure
The X-ray Emission of γ Cassiopeiae During the 2020-2021 Disc Eruption
International audienceContext. γ Cas is known for its unusually hard and intense X-ray emission. This emission could trace accretion by a compact companion, wind interaction with a hot sub-dwarf companion, or magnetic interaction between the star and its Be decretion disc. Aims: These various scenarios should lead to diverse dependences of the hard X-ray emission on disc density. To test these scenarios, we collected X-ray observations of γ Cas during an episode of enhanced disc activity that took place around January 2021. Methods: We investigate the variations in the disc properties using time series of dedicated optical spectroscopy and existing broadband photometry. Equivalent widths and peak velocity separations are measured for a number of prominent emission lines. Epoch-dependent Doppler maps of the Hα, Hβ, and He I λ 5876 emission lines are built to characterise the emission regions in velocity space. We analyse four XMM-Newton observations obtained between January 2021 and January 2022 at key phases of the episode of enhanced disc activity. Archival XMM-Newton, Chandra, MAXI, and RXTE-ASM data are also used to study the long-term correlation between optical and X-ray emission. Results: Optical spectroscopy unveils a clear increase in the radial extent of the emission regions during the episode of enhanced disc activity, whilst no increase in the V-band flux is recorded. Our Doppler maps do not reveal any stable feature in the disc resulting from the putative action of the companion on the outer parts of the Be disc. Whilst the hard X-ray emission is found to display the usual level and type of variability, no specific increase in the hard emission is observed in relation to the enhanced disc activity. However, at two occasions, including at the maximum disc activity, the soft X-ray emission of γ Cas is strongly attenuated, suggesting more efficient obscuration by material from a large flaring Be disc. In addition, there is a strong correlation between the long-term variations in the X-ray flux and the optical variations in the V-band photometry. Conclusions: The observed behaviour of γ Cas suggests no direct link between the properties of the outer regions of the Be disc and the hard X-ray emission, but it favours a link between the level of X-ray emission and the properties of the inner part of the Be disc. These results thus disfavour an accretion or colliding wind scenario
Doppler tomography of the circumstellar disk of
Aims. The work is aimed at studying the circumstellar disk of the bright
classical binary Be star π Aqr.
Methods. We analysed variations of a double-peaked profile of the
Hα emission line in the spectrum of π Aqr
that was observed in many phases during ~40 orbital cycles in 2004−2013. We applied the
discrete Fourier transform (DFT) method to search for periodicity in the peak intensity
ratio (V/R). Doppler tomography was used to study the structure of the disk around the
primary.
Results. The dominant frequency in the power spectrum of the
Hα V/R ratio is 0.011873 day-1, which
corresponds to a period of 84.2(2) days and agrees with the earlier determined orbital
period of the system, Porb = 84.1 days. The V/R shows a
sinusoidal variation that is phase-locked with the orbital period. Doppler maps of all our
spectra show a non-uniform structure of the disk around the primary: a ring with the inner
and outer radii at Vin ≈ 450 km s-1 and
Vout ≈ 200 km s-1, respectively, along with an
extended stable region (spot) at Vx ≈ 225
km s-1 and Vy ≈ 100
km s-1. The disk radius of ≈65   R⊙ = 0.33 AU was
estimated by assuming Keplerian motion of a particle on a circular orbit at the disk’s
outer edge
Evolution of the disk of π Aqr: From near-disappearance to a strong maximum
Some Be stars display important variability of the strength of the emission lines formed in their disk. This is notably the case of pi Aqr. We present here the recent evolution of the Be disk in this system thanks to spectra collected by amateur spectroscopists since the end of 2013. A large transition occurred: the emission linked to the Be disk nearly disappeared in January 2014, but the disk has recovered, with a line strength now reaching levels only seen during the active phase of 1950--1990. In parallel to this change in strength occurs a change of disk structure, notably involving the disappearance of the strong asymmetry responsible for the V/R modulation
The orbit and stellar masses of the archetype colliding-wind binary WR 140
International audienceWe present updated orbital elements for the Wolf-Rayet (WR) binary WR 140 (HD 193793; WC7pd + O5.5fc). The new orbital elements were derived using previously published measurements along with 160 new radial velocity measurements across the 2016 periastron passage of WR 140. Additionally, four new measurements of the orbital astrometry were collected with the CHARA Array. With these measurements, we derive stellar masses of and . We also include a discussion of the evolutionary history of this system from the Binary Population and Spectral Synthesis model grid to show that this WR star likely formed primarily through mass-loss in the stellar winds, with only a moderate amount of mass lost or transferred through binary interactions
Instrumental Methods for Professional and Amateur Collaborations in Planetary Astronomy
Amateur contributions to professional publications have increased exponentially over the last decades in the field of Planetary Astronomy. Here we review the different domains of the field in which collaborations between professional and amateur astronomers are effective and regularly lead to scientific publications. We discuss the instruments, detectors, softwares and methodologies typically used by amateur astronomers to collect the scientific data in the different domains of interest. Amateur contributions to the monitoring of planets and interplanetary matter, characterization of asteroids and comets, as well as the determination of the physical properties of Kuiper Belt Objects and exoplanets are discussed