101 research outputs found
Optical and UV spectroscopy of the peculiar RS CVn system, RT Lacertae
Spectra in the H-alpha and H-beta regions of the peculiar double-lined RS CVn binary, RT Lacertae, were obtained in the fall of 1984. Limited International Ultraviolet Explorer (IUE) long wavelength low and high resolution spectra were obtained concurrently. The ground based spectra have shown an asymmetry with orbital phase in the H-alpha profile. The H-beta profiles were consistent with the same effect. One hemisphere showed excess emission and the other excess absorption, with a broad Gaussian emission component superposed upon the excess H-alpha line. An improved radial velocity curve, giving a better determined mass ratio and geometry was derived. This combined with the radii implied by the rotational broadening of the spectra, showed one component to be 80 to 90% filling the equilibrium Roche surface. The two-faced nature is, therfore, very likely due to mass transfer from the contact component impacting upon its companion. Low resolution ultraviolet data showed that the supposed cooler component is bluer than its companion. High resolution ultraviolet data taken during secondary eclipse showed Mg II emission strength which decreased more slowly than the area visible. The phase behavior of the low resolution data support the former situation, indicating traditional chromospheric activity
On X-ray pulsations in beta Cephei-type variables
Beta Cephei-type variables are early B-type stars that are characterized by
oscillations observable in their optical light curves. At least one Beta
Cep-variable also shows periodic variability in X-rays. Here we study the X-ray
light curves in a sample of beta Cep-variables to investigate how common X-ray
pulsations are for this type of stars. We searched the Chandra and XMM-Newton
X-ray archives and selected stars that were observed by these telescopes for at
least three optical pulsational periods. We retrieved and analyzed the X-ray
data for kappa Sco, beta Cru, and alpha Vir. The X-ray light curves of these
objects were studied to test for their variability and periodicity. While there
is a weak indication for X-ray variability in beta Cru, we find no
statistically significant evidence of X-ray pulsations in any of our sample
stars. This might be due either to the insufficient data quality or to the
physical lack of modulations. New, more sensitive observations should settle
this question.Comment: accepted in A&
The XMM-Newton EPIC X-ray Light Curve Analysis of WR 6
We obtained four pointings of over 100 ks each of the well-studied Wolf-Rayet
star WR 6 with the XMM-Newton satellite. With a first paper emphasizing the
results of spectral analysis, this follow-up highlights the X-ray variability
clearly detected in all four pointings. However, phased light curves fail to
confirm obvious cyclic behavior on the well-established 3.766 d period widely
found at longer wavelengths. The data are of such quality that we were able to
conduct a search for "event clustering" in the arrival times of X-ray photons.
However, we fail to detect any such clustering. One possibility is that X-rays
are generated in a stationary shock structure. In this context we favor a
co-rotating interaction region (CIR) and present a phenomenological model for
X-rays from a CIR structure. We show that a CIR has the potential to account
simultaneously for the X-ray variability and constraints provided by the
spectral analysis. Ultimately, the viability of the CIR model will require both
intermittent long-term X-ray monitoring of WR 6 and better physical models of
CIR X-ray production at large radii in stellar winds.Comment: to appear in Ap
FK Comae Berenices, King of Spin: The COCOA-PUFS Project
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast
spinning, heavily spotted, yellow giant FK Com (HD117555; G4 III). This single
star is thought to be a recent binary merger, and is exceptionally active by
measure of its intense ultraviolet and X-ray emissions, and proclivity to
flare. COCOA-PUFS was carried out with Hubble Space Telescope in the UV
(120-300 nm), using mainly its high-performance Cosmic Origins Spectrograph,
but also high-precision Space Telescope Imaging Spectrograph; Chandra X-ray
Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy
Transmission Grating Spectrometer; together with supporting photometry and
spectropolarimetry in the visible from the ground. This is an introductory
report on the project.
FK Com displayed variability on a wide range of time scales, over all
wavelengths, during the week-long main campaign, including a large X-ray flare;
"super-rotational broadening" of the far-ultraviolet "hot-lines" (e.g., Si IV
139 nm (T~80,000 K) together with chromospheric Mg II 280 nm and C II 133 nm
(10,000-30,000 K); large Doppler swings suggestive of bright regions
alternately on advancing and retreating limbs of the star; and substantial
redshifts of the epoch-average emission profiles. These behaviors paint a
picture of a highly extended, dynamic, hot (10 MK) coronal magnetosphere around
the star, threaded by cooler structures perhaps analogous to solar prominences,
and replenished continually by surface activity and flares. Suppression of
angular momentum loss by the confining magnetosphere could temporarily postpone
the inevitable stellar spindown, thereby lengthening this highly volatile stage
of coronal evolution.Comment: to be published in ApJ
Heating in an Extended Accretion Disk Corona along the Z-Pattern in Cyg X-2
We observed at very high spectral resolution the prototype Z-source Cyg x-2
twice along its entire X-ray spectral variation pattern. In this preliminary
analysis we find an extended accretion disk corona exhibiting Lyman alpha
emissions from various H-like ions, as well as emissions from He-like ions of
Fe and Al, and Li-like ions of Fe. The brightest lines show a range of line
broadening: H-like lines are very broad with Doppler velocities between 1100
and 2700 km/s, while some others are narrower with widths of a few hundred
km/s. Line diagnostics allow us for the first time to determine coronal
parameters. The line properties are consistent with a stationary, extended up
to 10^10 cm, dense (1x10^15 cm^-3), and hot (log xi > 3; T > 10^6 K) accretion
disk corona. We find ongoing heating of the corona along the Z-track and
determine that heating luminosities change from about 0.4 L_Edd on the
horizontal to about 1.4 L_Edd on the flaring branch.Comment: 4 pages, 3 figures, ApJ Letters submitte
A Three Micron Survey of the Chamaeleon I Dark Cloud
We describe an L-band photometric survey of 0.5 square deg of the Cha I dark
cloud. The survey has a completeness limit of L < 11.0. Our survey detects 124
sources, including all known pre-main sequence stars with L < 11. The fraction
of sources with near-IR excess emission is 58% +- 4% for K = 9-11. Cha I
sources have bluer H-K and K-L colors than pre-main sequence stars in
Taurus-Auriga. These sources also have a strong correlation between EW(H-alpha)
and K-L. Stars with K-L 0.6
have strong H-alpha emission. Because many Cha I sources are heavily reddened,
this division between weak emission T Tauri stars and classical T Tauri stars
occurs at a redder K-L than in Taurus-Auriga.Comment: 12 pages of text, 4 figures, and 1 three page table of data modified
version adds reference and acknowledgemen
The close T Tauri binary system V4046 Sgr: Rotationally modulated X-ray emission from accretion shocks
We report initial results from a quasi-simultaneous X-ray/optical observing
campaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauri
star (CTTS) binary in which both components are actively accreting. V4046 Sgr
is a strong X-ray source, with the X-rays mainly arising from high-density (n_e
~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelength
campaign aims to simultaneously constrain the properties of this X-ray emitting
plasma, the large scale magnetic field, and the accretion geometry. In this
paper, we present key results obtained via time-resolved X-ray grating spectra,
gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotations.
We find that the emission lines produced by this high-density plasma display
periodic flux variations with a measured period, 1.22+/-0.01 d, that is
precisely half that of the binary star system (2.42 d). The observed rotational
modulation can be explained assuming that the high-density plasma occupies
small portions of the stellar surfaces, corotating with the stars, and that the
high-density plasma is not azimuthally symmetrically distributed with respect
to the rotational axis of each star. These results strongly support models in
which high-density, X-ray-emitting CTTS plasma is material heated in accretion
shocks, located at the base of accretion flows tied to the system by magnetic
field lines.Comment: paper accepted by Ap
- …