40 research outputs found
Short period line profile and light variations in the Be star ω Orionis
We present the results of a multisite spectroscopic and photometric campaign on the Be star ω Orionis. From the photometry and radial velocity variation of several spectral lines, we confirm that the star is a variable with period . Only one period can be extracted from both the photometric and radial velocity observations. We find that the projected rotational velocity from the helium lines is considerably smaller than from the metal lines . The line profiles show an excess absorption feature moving from blue to red for half the period and from red to blue for the other half of the period. Another excess absorption feature moves exactly out of phase. The excess absorption features are present in photospheric lines as well as in lines which are significantly affected by circumstellar material, such as Hβ. From this we conclude that the periodic variations are most probably associated with corotating circumstellar materia
Classical Cepheids: Yet another version of the Baade-Becker-Wesselink method
We propose a new version of the Baade--Becker--Wesselink technique, which
allows one to independently determine the colour excess and the intrinsic
colour of a radially pulsating star, in addition to its radius, luminosity, and
distance. It is considered to be a generalization of the Balona approach. The
method also allows the function F(CI) = BC + 10 log (Teff) for the class of
pulsating stars considered to be calibrated. We apply this technique to a
number of classical Cepheids with very accurate light and radial-velocity
curves and with bona fide membership in open clusters (SZ Tau, CF Cas, U Sgr,
DL Cas, GY Sge), and find the results to agree well with the reddening
estimates of the host open clusters. The new technique can also be applied to
other pulsating variables, e.g. RR Lyrae and RV Tauri.Comment: 6 pages, 2 figures, 1 table; Submitted to Astrophysical Bulletin,
201
The Planetary Nebula Luminosity Function at the Dawn of Gaia
The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
The Kepler characterization of the variability among A- and F-type stars. - I: General overview
Red Clump stars in
We measure the large frequency separation, Δν, and the frequency of maximum amplitude, νmax, for 10 Red Clump (RC) single member (SM) stars in the Kepler open cluster NGC 6819. We derive luminosities and masses for each individual RC star. A comparison of the observations with an isochrone of Age = 2.5 Gyr, Z = 0.017 with no mass loss using a statistical techniques is made. A fractional mass loss of 5 ± 3 percent is obtained if we assume that no correction to Δν between RC and red-giant branch (RGB) is necessary. However, models suggest that an effective correction of about 1.9 percent in Δν is required to obtain the correct mass of RC stars owing to the different internal structures of stars in the two evolutionary stages. In this case we find that the mass loss in the red giant branch is not significantly different from zero. This finding confirms that of [6]. It is clear that the mass estimate obtained by asteroseismology is not sufficient to deduce the mass loss on the red giant branch. However, it is clearly only a few percent at most