19 research outputs found
DDO spectroscopic survey of MOST variable stars
A spectroscopic support survey of 103 objects observed by the MOST satellite
is presented; 96 are variable stars with 83 of them being new MOST
variable-star detections or stars with variability types verified and/or
modified on the basis of the MOST data. Analysis of 241 medium-resolution
spectra using the broadening-functions formalism yielded radial velocities,
projected rotational velocities (for 31 targets for which it was possible) and
spectral type estimates. Seven new spectroscopic binaries were discovered;
orbital solutions are given for two of them (HD73709, and GSC 0814-0323). The
visual binary HD46180 was found to be composed of two close binary stars
(eclipsing and non-eclipsing one) very probably forming a physical quadruple
system.Comment: 2 figures, accepted to MNRAS on October 17, 200
The Araucaria Project: A study of the classical Cepheid in the eclipsing binary system OGLE LMC562.05.9009 in the Large Magellanic Cloud
We present a detailed study of the classical Cepheid in the double-lined,
highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a
fundamental mode pulsator with a period of 2.988 days. The orbital period of
the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes
and photometry spanning 22 years, we were able to derive the dynamical masses
and radii of both stars with exquisite accuracy. Both stars in the system are
very similar in mass, radius and color, but the companion is a stable,
non-pulsating star. The Cepheid is slightly more massive and bigger (M_1 = 3.70
+/- 0.03M_sun, R_1 = 28.6 +/- 0.2R_sun) than its companion (M_2 = 3.60 +/-
0.03M_sun, R_2 = 26.6 +/- 0.2R_sun). Within the observational uncertainties
both stars have the same effective temperature of 6030 +/- 150K. Evolutionary
tracks place both stars inside the classical Cepheid instability strip, but it
is likely that future improved temperature estimates will move the stable giant
companion just beyond the red edge of the instability strip. Within current
observational and theoretical uncertainties, both stars fit on a 205 Myr
isochrone arguing for their common age. From our model, we determine a value of
the projection factor of p = 1.37 +/- 0.07 for the Cepheid in the
OGLE-LMC562.05.9009 system. This is the second Cepheid for which we could
measure its p-factor with high precision directly from the analysis of an
eclipsing binary system, which represents an important contribution towards a
better calibration of Baade-Wesselink methods of distance determination for
Cepheids.Comment: Accepted to be published in Ap
Photometric Observations of Three High Mass X-Ray Binaries and a Search for Variations Induced by Orbital Motion
We searched for long period variation in V-band, Ic-band and RXTE X-ray light
curves of the High Mass X-ray Binaries (HMXBs) LS 1698 / RX J1037.5-5647, HD
110432 / 1H 1249-637 and HD 161103 / RX J1744.7-2713 in an attempt to discover
orbitally induced variation. Data were obtained primarily from the ASAS
database and were supplemented by shorter term observations made with the 24-
and 40-inch ANU telescopes and one of the robotic PROMPT telescopes. Fourier
periodograms suggested the existence of long period variation in the V-band
light curves of all three HMXBs, however folding the data at those periods did
not reveal convincing periodic variation. At this point we cannot rule out the
existence of long term V-band variation for these three sources and hints of
longer term variation may be seen in the higher precision PROMPT data. Long
term V-band observations, on the order of several years, taken at a frequency
of at least once per week and with a precision of 0.01 mag, therefore still
have a chance of revealing long term variation in these three HMXBs.Comment: Accepted, RAA, May, 201
The atmosphere, the p-factor and the bright visible circumstellar environment of the prototype of classical Cepheids ÎŽ Cep
Even â 16000 cycles after its discovery by John Goodricke in 1783, ÎŽ Cep, the prototype of classical Cepheids, is still studied intensively in order to better understand its atmospheric dynamical structure and its environment. Using HARPS-N spectroscopic measurements, we have measured the atmospheric velocity gradient of ÎŽ Cep for the first time and we confirm the decomposition of the projection factor, a subtle physical quantity limiting the Baade-Wesselink (BW) method of distance determination. This decomposition clarifies the physics behind the projection factor and will be useful to interpret the hundreds of p-factors that will come out from the next Gaia release. Besides, VEGA/CHARA interferometric observations of the star revealed a bright visible circumstellar environment contributing to about 7% to the total flux. Better understanding the physics of the pulsation and the environment of Cepheids is necessary to improve the BW method of distance determination, a robust tool to reach Cepheids in the MilkyWay, and beyond, in the Local Group
CUBES : the Cassegrain U-band Efficient Spectrograph
In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (> 40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R >20, 000 (with a lower-resolution, sky-limited mode of R ~7, 000). With the design focusing on maximizing the instrument throughput (ensuring a Signal to Noise Ratio (SNR) ~20 per high-resolution element at 313 nm for U ~18.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the detailed design and construction phase. First science operations are planned for 2028