8,797 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
Amplitude variations of modulated RV Tauri stars support the dust obscuration model of the RVb phenomenon
Context. RV Tauri-type variables are pulsating post-AGB stars that evolve
rapidly through the instability strip after leaving the Asymptotic Giant
Branch. Their light variability is dominated by radial pulsations. Members of
the RVb subclass show an additional variability in form of a long-term
modulation of the mean brightness, for which the most popular theories all
assume binarity and some kind of circumstellar dust. Here we address if the
amplitude modulations are consistent with the dust obscuration model. Aims. We
measure and interpret the overall changes of the mean amplitude of the
pulsations along the RVb variability. Methods. We compiled long-term
photometric data for RVb-type stars, including visual observations of the
American Association of Variable Star Observers, ground-based CCD photometry
from the OGLE and ASAS projects and ultra-precise space photometry of one star,
DF Cygni, from the Kepler space telescope. After converting all the
observations to flux units, we measure the cycle-to-cycle variations of the
pulsation amplitude and correlate them to the actual mean fluxes. Results. We
find a surprisingly uniform correlation between the pulsation amplitude and the
mean flux: they scale linearly with each other for a wide range of fluxes and
amplitudes. It means that the pulsation amplitude actually remains constant
when measured relative to the system flux level. The apparent amplitude
decrease in the faint states has long been noted in the literature but it was
always claimed to be difficult to explain with the actual models of the RVb
phenomenon. Here we show that when fluxes are used instead of magnitudes, the
amplitude attenuation is naturally explained by periodic obscuration from a
large opaque screen, one most likely corresponding to a circumbinary dusty disk
that surrounds the whole system.Comment: 8 pages, 6 figures, accepted for publication in A&
Red variables in the OGLE-II database. I. Pulsations and period-luminosity relations below the tip of the Red Giant Branch of the LMC
We present period-luminosity relations for more than 23,000 red giants in the
Large Magellanic Cloud observed by the OGLE-II microlensing project. The OGLE
period values were combined with the 2MASS single-epoch JHK photometric data.
For the brighter stars we find agreement with previous results (four different
sequences corresponding to different modes of pulsation in AGB stars). We also
discovered two distinct and well-separated sequences below the tip of the Red
Giant Branch. They consist of almost 10,000 short-period (15 d <P< 50 d),
low-amplitude (A_I<0.04 mag) red variable stars, for which we propose that a
significant fraction is likely to be on the Red Giant Branch, showing radial
pulsations in the second and third overtone modes. The excitation mechanism
could be either Mira-like pulsation or solar-like oscillations driven by
convection.Comment: 5 pages, 4 figures; accepted for publication in MNRAS (Pink Pages);
proof corrections adde
Pushing the limits: K2 observations of the trans-Neptunian objects 2002 GV31 and (278361) 2007 JJ43
We present the first photometric observations of trans-Neptunian objects
(TNOs) taken with the Kepler space telescope, obtained in the course of the K2
ecliptic survey. Two faint objects have been monitored in specifically designed
pixel masks that were centered on the stationary points of the objects, when
their daily motion was the slowest. In the design of the experiment, only the
apparent path of these objects were retrieved from the detectors, i.e. the
costs in terms of Kepler pixels were minimized. Because of the faintness of the
targets we employ specific reduction techniques and co-added images. We measure
rotational periods and amplitudes in the unfiltered Kepler band as follows: for
(278361) 2007 JJ43 and 2002 GV31 we get P_rot=12.097 h and P_rot=29.2 h while
0.10 and 0.35 mag for the total amplitudes, respectively. Future space
missions, like TESS and PLATO are not well suited to this kind of observations.
Therefore, we encourage to include the brightest TNOs around their stationary
points in each observing campaign to exploit this unique capability of the K2
Mission -- and therefore to provide unbiased rotational, shape and albedo
characteristics of many objects.Comment: Accepted for publication in ApJ Letters, 5.2 pages in emulateapj
style, misspelled 2007 JJ43 designation correcte
CCD photometry and new models of 5 minor planets
We present new R filtered CCD observations of 5 faint and moderately faint
asteroids carried out between October, 1998 and January, 1999. The achieved
accuracy is between 0.01-0.03 mag, depending mainly on the target brightness.
The obtained sinodic periods and amplitudes:
683 Lanzia - 4.6+/-0.2 h, 0.13 mag; 725 Amanda - >3.0 h, >=0.40 mag; 852
Wladilena - 4.62+/-0.01 h, 0.32 mag (December, 1998) and 0.27 mag (January,
1999); 1627 Ivar - 4.80+/-0.01, 0.77 mag (December, 1998) and 0.92 mag
(January, 1999). The Near Earth Object 1998 PG unambiguously showed
doubly-periodic lightcurve, suggesting the possibility of a relatively fast
precession (P_1=1.3 h, P_2=5.3 h).
Collecting all data from the literature, we determined new models for 3 minor
planets. The resulting spin vectors and triaxial ellipsoids have been
calculated by an amplitude-method. Sidereal periods and senses of rotation were
calculated for two asteroids (683 and 1627) by a modified epoch-method. The
results are:
683 - lambda_p=15/195+/-25 deg, beta_p=52+/-15 deg, a/b=1.15+/-0.05,
b/c=1.05+/-0.05, P_sid=0.1964156+/-0.0000001 d, retrograde; 852 -
lambda_p=30/210+/-20 deg, beta_p=30+/-10 deg, a/b=2.3+/-0.3, b/c=1.2+/-0.2;
1627 - lambda_p=145/325+/-8 deg, beta_p=34+/-6 deg, a/b=2.0+/-0.1,
b/c=1.09+/-0.05, P_sid=0.1999154+/-0.0000003 d, retrograde. The obtained shape
of 1627 is in good agreement with radar images by Ostro et al. (1990).Comment: 8 pages, accepted for publication in Astronomy and Astrophysics
Suppl. Serie
Asymmetric fundamental band CO lines as a sign of an embedded giant planet
We investigate the formation of double-peaked asymmetric line profiles of CO
in the fundamental band spectra emitted by young (1-5Myr) protoplanetary disks
hosted by a 0.5-2 Solar mass star. Distortions of the line profiles can be
caused by the gravitational perturbation of an embedded giant planet with q=4.7
10^-3 stellar-to-planet mass ratio. Locally isothermal, 2D hydrodynamic
simulations show that the disk becomes globally eccentric inside the planetary
orbit with stationary ~0.2-0.25 average eccentricity after ~2000 orbital
periods. For orbital distances 1-10 AU, the disk eccentricity is peaked inside
the region where the fundamental band of CO is thermal excitated. Hence, these
lines become a sensitive indicators of the embedded planet via their
asymmetries (both in flux and wavelength). We find that the line shape
distortions (e.g. distance, central dip, asymmetry and positions of peaks) of a
given transition depend on the excitation energy (i.e. on the rotational
quantum number J). The magnitude of line asymmetry is increasing/decreasing
with J if the planet orbits inside/outside the CO excitation zone (R_CO<=3, 5
and 7 AU for a 0.5,1 and 2 Solar mass star, respectively), thus one can
constrain the orbital distance of a giant planet by determining the slope of
peak asymmetry-J profile. We conclude that the presented spectroscopic
phenomenon can be used to test the predictions of planet formation theories by
pushing the age limits for detecting the youngest planetary systems.Comment: 7 pages, 5 figures, to appear in ApJ
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
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