6,896 research outputs found
A photometric and spectroscopic study of the brightest northern Cepheids. III. A high-resolution view of Cepheid atmospheres
We present new high-resolution (R=40000) spectroscopic observations of 18
bright northern Cepheids carried out at David Dunlap Observatory, in 1997. The
measurements mainly extend those of presented in Paper I adding three more
stars (AW Per, SV Vul, T Mon). The spectra were obtained in the interval of
5900 A and 6660 A. New radial velocities determined with the cross-correlation
technique and the bisector technique are presented. We found systematic
differences between the spectroscopic and CORAVEL-type measurements as large as
1-3 km/s in certain phases. We performed Baade-Wesselink analysis for CK Cam
discovered by the Hipparcos satellite. The resulting radius is 31+/-1 Ro, which
is in very good agreement with recent period-radius relation by Gieren et al.
(1999). Observational pieces of evidence of possible velocity gradient
affecting the individual line profiles are studied. The FWHM of the metallic
lines, similarly to the velocity differences, shows a very characteristic phase
dependence, illustrating the effect of global compression in the atmosphere.
The smallest line widths always occur around the maximal radius, while the
largest FWHM is associated with the velocity reversal before the minimal
radius. Three first overtone pulsators do not follow the general trend: the
largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the
expansion, while in V1334 Cyg there are only barely visible FWHM-variations.
The possibility of a bright yellow companion of V1334 Cyg is briefly discussed.
The observed line profile asymmetries can be partly associated with the
velocity gradient, which is also supported by the differences between
individual line velocities of different excitation potentials.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Mass and orbit constraints of the gamma-ray binary LS 5039
We present the results of space-based photometric and ground-based
spectroscopic observing campaigns on the gamma-ray binary LS 5039. The new
orbital and physical parameters of the system are similar to former results,
except we found a lower eccentricity. Our MOST-data show that any broad-band
optical photometric variability at the orbital period is below the 2 mmag
level. Light curve simulations support the lower value of eccentricity and
imply that the mass of the compact object is higher than 1.8 solar masses.Comment: 2 pages, 1 figure (with 2 panels); to be published in the
Proceedings: From Interacting Binaries to Exoplanets: Essential Modeling
Tools, IAU Symposium 282 (18-22 July, 2011, Tatranska Lomnica, Slovakia
Discovery of the spectroscopic binary nature of six southern Cepheids
We present the analysis of photometric and spectroscopic data of six bright
Galactic Cepheids: GH Carinae, V419 Centauri, V898 Centauri, AD Puppis, AY
Sagittarii, and ST Velorum. Based on new radial velocity data (in some cases
supplemented with earlier data available in the literature), these Cepheids
have been found to be members in spectroscopic binary systems. V898 Cen turned
out to have one of the largest orbital radial velocity amplitude (> 40 km/s)
among the known binary Cepheids. The data are insufficient to determine the
orbital periods nor other orbital elements for these new spectroscopic
binaries.
These discoveries corroborate the statement on the high frequency of
occurrence of binaries among the classical Cepheids, a fact to be taken into
account when calibrating the period-luminosity relationship for Cepheids.
We have also compiled all available photometric data that revealed that the
pulsation period of AD Pup, the longest period Cepheid in this sample, is
continuously increasing with Delta P = 0.004567 d/century, likely to be caused
by stellar evolution. The wave-like pattern superimposed on the parabolic O-C
graph of AD Pup may well be caused by the light-time effect in the binary
system. ST Vel also pulsates with a continuously increasing period. The other
four Cepheids are characterised with stable pulsation periods in the last half
century.Comment: accepted by the MNRAS, 11 pages, 16 figures, 18 tables, a part of the
data can be downloaded from the online version of this articl
Nova Cygni 2001/2 = V2275 Cyg
We present an analysis of low- and medium resolution spectra of the very fast
nova, Nova Cygni 2001/2 (V2275 Cyg) obtained at nine epochs in August,
September and October, 2001. The expansion velocity from hydrogen Balmer lines
is found to be 2100 km/s, although early H-alpha profile showed a weak feature
at -3500 km/s, too. The overall appearance of the optical spectrum is dominated
by broad lines of H, He and N, therefore, the star belongs to the ``He/N''
subclass of novae defined by Williams (1992). Interstellar lines and bands, as
well as BV photometry taken from the literature yielded to a fairly high
reddening of E(B-V)=1.0+/-0.1 mag. The visual light curve was used to deduce
M_V by the maximum magnitude versus rate of decline relationship. The resulting
parameters are: t_0=2452141.4(+0.1)(-0.5), t_2=2.9+/-0.5 days, t_3=7+/-1 days,
M_V=-9.7+/-0.7 mag. Adopting these parameters, the star lies between 3 kpc and
8 kpc from the Sun.Comment: 5 pages, 5 figures, accepted for publication in A&
Discovery of the spectroscopic binary nature of three bright southern Cepheids
We present an analysis of spectroscopic radial velocity and photometric data
of three bright Galactic Cepheids: LR Trianguli Australis (LR TrA), RZ Velorum
(RZ Vel), and BG Velorum (BG Vel). Based on new radial velocity data, these
Cepheids have been found to be members of spectroscopic binary systems.
The ratio of the peak-to-peak radial velocity amplitude to photometric
amplitude indicates the presence of a companion for LR TrA and BG Vel. IUE
spectra indicate that the companions of RZ Vel and BG Vel cannot be hot stars.
The analysis of all available photometric data revealed that the pulsation
period of RZ Vel and BG Vel varies monotonically, due to stellar evolution.
Moreover, the longest period Cepheid in this sample, RZ Vel, shows period
fluctuations superimposed on the monotonic period increase. The light-time
effect interpretation of the observed pattern needs long-term photometric
monitoring of this Cepheid. The pulsation period of LR TrA has remained
constant since the discovery of its brightness variation.
Using statistical data, it is also shown that a large number of spectroscopic
binaries still remain to be discovered among bright classical Cepheids.Comment: 9 pages, 14 figure
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