Abstract
Eta Carinae (
η
Car) exhibits a unique set of P Cygni profiles with both broad and narrow components. Over many decades, the spectrum has changed—there has been an increase in observed ...continuum fluxes and a decrease in Fe
ii
and H
i
emission-line equivalent widths. The spectrum is evolving toward that of a P Cygni star such as P Cygni itself and HDE 316285. The spectral evolution has been attributed to intrinsic variations such as a decrease in the mass-loss rate of the primary star or differential evolution in a latitudinal-dependent stellar wind. However, intrinsic wind changes conflict with three observational results: the steady long-term bolometric luminosity; the repeating X-ray light curve over the binary period; and the constancy of the dust-scattered spectrum from the Homunculus. We extend previous work that showed a secular strengthening of P Cygni absorptions by adding more orbital cycles to overcome temporary instabilities and by examining more atomic transitions.
cmfgen
modeling of the primary wind shows that a time-decreasing mass-loss rate is not the best explanation for the observations. However, models with a
small
dissipating absorber in our line of sight can explain both the increase in brightness and changes in the emission and P Cygni absorption profiles. If the spectral evolution is caused by the dissipating circumstellar medium, and not by intrinsic changes in the binary, the dynamical timescale to recover from the Great Eruption is much less than a century, different from previous suggestions.
X-ray response to disc evolution in two γ Cas stars Nazé, Yaël; Rauw, Gregor; Bohlsen, Terrence ...
Monthly Notices of the Royal Astronomical Society,
05/2022, Letnik:
512, Številka:
2
Journal Article, Web Resource
Recenzirano
Odprti dostop
ABSTRACT
The Hα emission of a set of southern γ Cas stars was monitored since 2019, with the aim of detecting transition events and examining how their peculiar X-ray emission would react in such ...cases. Two stars, namely HD 119682 and V767 Cen, were found to display slowly decreasing disc emissions. These decreases were not perfectly monotonic and several temporary and limited rebuilding events were observed. For HD 119682, the emission component in Hα disappeared in 2020 mid-July. In X-rays, the X-ray flux was twice smaller than that recorded two decades ago but of a similar level as observed a decade ago. The X-ray flux decreased over the campaign by 30 per cent, but the hardness remained similar in data sets of all epochs. In particular, the γ Cas character remained as clear as before even when there was no trace of disc emission in the Hα line. For V767 Cen, the full disappearance of disc emission in Hα never occurred. We followed closely a disc rebuilding event, but no significant change in flux or hardness was detected. These behaviours are compared to those of other γ Cas stars and their consequences on the X-ray generation are discussed.
ABSTRACT We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system δ Ori A, consisting ...of a binary O9.5II+early-B (Aa1 and Aa2) with P = 5.7 days, and a more distant tertiary (O9 IV years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV) curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.
We report on the results of our optical photometric observations of a black hole X-ray binary, V4641 Sgr during an outburst in 2003 August. During the outburst, we detected several properties having ...noteworthy similarities to those observed during an outburst in 2002 May; the outburst lasted about 6 days, during which it exhibited flares and rapid fluctuations, having timescales of
$10^{2\hbox{--}4} \,\mathrm{s}$
. In complicated profiles of light curves, we identified several recurring patterns, which were also observed during the 2002 outburst. First, the object frequently experienced sudden temporary fadings, which we call “dips”, appearing just after the states characterized by strong short-term fluctuations. Second, we detected optical flashes, which are characterized by a brightening by
$\sim 0.5 \,\mathrm{mag}$
within
$\sim 50 \,\mathrm{s}$
. Based on the similarity of the outbursts in 2002 and 2003, we conclude that they have the same nature. This is the first time that repetitive outburst phenomena have been confirmed in V4641 Sgr. The object probably has an outburst interval that can be as small as 1–2 years.
We photometrically observed four southern dwarf novae in outburst (NSV 10934, MM Sco, AB Nor and CAL 86). NSV 10934 was confirmed to be an SU UMa-type dwarf nova with a mean superhump period of ...0.07478(1) d. This star also showed transient appearance of quasi-periodic oscillations during the final growing stage of the superhumps. Combined with the recent theoretical interpretation and with the rather unusual rapid terminal fading of normal outbursts, NSV 10934 may be a candidate intermediate polar showing SU UMa-type properties. The mean superhump periods of MM Sco and AB Nor were determined to be 0.06136(4) and 0.08438(2) d, respectively. We suggest that AB Nor belongs to a rather rare class of long-period SU UMa-type dwarf novae with low mass-transfer rates. We also observed an outburst of the suspected SU UMa-type dwarf nova CAL 86. We identified this outburst as a normal outburst and determined the mean decline rate of 1.1 mag d−1.
The Halpha emission of a set of southern gamma-Cas stars was monitored since 2019, with the aim of detecting transition events and examining how their peculiar X-ray emission would react in such ...cases. Two stars, HD119682 and V767Cen, were found to display slowly decreasing disk emissions. These decreases were not perfectly monotonic and several temporary and limited re-building events were observed. For HD119682, the emission component in Halpha disappeared in mid-July 2020. In X-rays, the X-ray flux was twice smaller than recorded two decades ago but of a similar level as observed a decade ago. The X-ray flux decreased over the campaign by 30%, but the hardness remained similar in datasets of all epochs. In particular, the gamma-Cas character remained as clear as before even when there was no trace of disk emission in the Halpha line. For V767Cen, the full disappearance of disk emission in Halpha never occurred. We followed closely a disk rebuilding event, but no significant change in flux or hardness was detected. These behaviours are compared to those of other gamma-Cas stars and their consequences on the X-ray generation are discussed.
We report on the first multi-color precision light curve of the bright
Wolf-Rayet binary $\gamma^2$ Velorum, obtained over six months with the
nanosatellites in the BRITE- Constellation fleet. In ...parallel, we obtained 488
high-resolution optical spectra of the system. In this first report on the
datasets, we revise the spectroscopic orbit and report on the bulk properties
of the colliding winds. We find a dependence of both the light curve and excess
emission properties that scales with the inverse of the binary separation. When
analyzing the spectroscopic properties in combination with the photometry, we
find that the phase dependence is caused only by excess emission in the lines,
and not from a changing continuum. We also detect a narrow, high-velocity
absorption component from the He I $\lambda$5876 transition, which appears
twice in the orbit. We calculate smoothed-particle hydrodynamical simulations
of the colliding winds and can accurately associate the absorption from He I to
the leading and trailing arms of the wind shock cone passing tangentially
through our line of sight. The simulations also explain the general strength
and kinematics of the emission excess observed in wind lines such as C III
$\lambda$5696 of the system. These results represent the first in a series of
investigations into the winds and properties of $\gamma^2$ Velorum through
multi-technique and multi-wavelength observational campaigns.
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