360 research outputs found
Long Period Variable Stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used to calibrate
both infrared luminosities and kinematical parameters of Long Period Variable
stars (LPVs). Individual absolute K and IRAS 12 and 25 luminosities of 800 LPVs
are determined and made available in electronic form.
The estimated mean kinematics is analyzed in terms of galactic populations.
LPVs are found to belong to galactic populations ranging from the thin disk to
the extended disk. An age range and a lower limit of the initial mass is given
for stars of each population. A difference of 1.3mag in K for the upper limit
of the Asymptotic Giant Branch is found between the disk and old disk galactic
populations, confirming its dependence on the mass in the main sequence.
LPVs with a thin envelope are distinguished using the estimated mean IRAS
luminosities. The level of attraction (in the classification sense) of each
group for the usual classifying parameters of LPVs (variability and spectral
types) is examined.Comment: Accepted for publication in A&A (May 2001). 13 page
Field #3 of the Palomar-Groningen Survey II. Near-infrared photometry of semiregular variables
Near-infrared photometry (JHKL'M) was obtained for 78 semiregular variables
(SRVs) in field #3 of the Palomar-Groningen survey (PG3, l=0, b=-10). Together
with a sample of Miras in this field a comparison is made with a sample of
field SRVs and Miras. The PG3 SRVs form a sequence (period-luminosity
& period-colour) with the PG3 Miras, in which the SRVs are the short period
extension to the Miras. The field and PG3 Miras follow the same P/(J--K)o
relation, while this is not the case for the field and PG3 SRVs. Both the PG3
SRVs and Miras follow the SgrI period-luminosity relation adopted from Glass et
al. (1995, MNRAS 273, 383). They are likely pulsating in the fundamental mode
and have metallicities spanning the range from intermediate to approximately
solar.Comment: 14 pages LaTeX (2 tables, 8 figures), to appear in A&A 338 (1998);
minor modifications in tex
ALMA observations of the variable 12CO/13CO ratio around the asymptotic giant branch star R Sculptoris
[abridged] The 12CO/13CO ratio is often used as a measure of the 12C/13C
ratio in the circumstellar environment, carrying important information about
the stellar nucleosynthesis. External processes can change the 12CO and 13CO
abundances, and spatially resolved studies of the 12CO/13CO ratio are needed to
quantify the effect of these processes on the globally determined values.
Additionally, such studies provide important information on the conditions in
the circumstellar environment. The detached-shell source R Scl, displaying CO
emission from recent mass loss, in a binary-induced spiral structure as well as
in a clumpy shell produced during a thermal pulse, provides a unique laboratory
for studying the differences in CO isotope abundances throughout its recent
evolution. We observed both the 12CO(J=3-2) and the 13CO(J=3-2) line using
ALMA. We find significant variations in the 12CO/13CO intensity ratios and
consequently in the abundance ratios. The average CO isotope abundance ratio is
at least a factor three lower in the shell (~19) than that in the present-day
(60). Additionally, variations in the ratio of more
than an order of magnitude are found in the shell itself. We attribute these
variations to the competition between selective dissociation and isotope
fractionation in the shell, of which large parts cannot be warmer than ~35 K.
However, we also find that the 12CO/13CO ratio in the present-day mass loss is
significantly higher than the 12C/13C ratio determined in the stellar
photosphere from molecular tracers (~19). The origin of this discrepancy is
still unclear, but we speculate that it is due to an embedded source of
UV-radiation that is primarily photo-dissociating 13CO. This radiation source
could be the hitherto hidden companion. Alternatively, the UV-radiation could
originate from an active chromosphere of R Scl itself....Comment: 6 pages, 5 figures, online data available at
http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/A+A/556/L
Hipparcos period-luminosity relations for Miras and semiregular variables
We present period-luminosity diagrams for nearby Miras and semiregulars,
selecting stars with parallaxes better than 20 per cent and well-determined
periods. Using K-band magnitudes, we find two well-defined P-L sequences, one
corresponding to the standard Mira P-L relation and the second shifted to
shorter periods by a factor of about 1.9. The second sequence only contains
semiregular variables, while the Mira sequence contains both Miras and
semiregulars. Several semiregular stars show double periods in agreement with
both relations. The Whitelock evolutionary track is shown to fit the data,
indicating that the semiregulars are Mira progenitors. The transition between
the two sequences may correspond to a change in pulsation mode or to a change
in the stellar structure. Large amplitude pulsations leading to classical Mira
classification occur mainly near the tip of the local AGB luminosity function.Comment: 10 pages with figures, accepted by ApJ Letter
The detached dust shells of AQ And, U Ant, and TT Cyg
Detached circumstellar dust shells are detected around three carbon variables
using Herschel-PACS. Two of them are already known on the basis of their
thermal CO emission and two are visible as extensions in IRAS imaging data. By
model fits to the new data sets, physical sizes, expansion timescales, dust
temperatures, and more are deduced. A comparison with existing molecular CO
material shows a high degree of correlation for TT Cyg and U Ant but a few
distinct differences with other observables are also found.Comment: Letter accepted for publication on the A&A Herschel Special Issu
Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
The asymptotic giant branch star R Sculptoris is surrounded by a detached
shell of dust and gas. The shell originates from a thermal pulse during which
the star undergoes a brief period of increased mass loss. It has hitherto been
impossible to constrain observationally the timescales and mass-loss properties
during and after a thermal pulse - parameters that determine the lifetime on
the asymptotic giant branch and the amount of elements returned by the star.
Here we report observations of CO emission from the circumstellar envelope and
shell around R Sculptoris with an angular resolution of 1.3 arcsec. What was
hitherto thought to be only a thin, spherical shell with a clumpy structure, is
revealed to contain a spiral structure. Spiral structures associated with
circumstellar envelopes have been seen previously, from which it was concluded
that the systems must be binaries. Using the data, combined with hydrodynamic
simulations, we conclude that R Sculptoris is a binary system that underwent a
thermal pulse approximately 1800 years ago, lasting approximately 200 years.
About 0.003 Msun of mass was ejected at a velocity of 14.3 km s-1 and at a rate
approximately 30 times higher than the prepulse mass-loss rate. This shows that
approximately 3 times more mass is returned to the interstellar medium during
and immediately after a pulse than previously thought.Comment: Accepted by Natur
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