129 research outputs found
Improved SAAOâ2MASS photometry transformations
Near-infrared photometry of 599 stars is used to calculate transformations from the South
African Astronomical Observatory (SAAO) JHK system to the Two-Micron All-Sky Survey
(2MASS) JHKS system. Both several-term formal regression relations and simplified transformations
are presented. Inverse transformations (i.e. 2MASS to SAAO) are also given. The
presence of non-linearities in some colour terms is highlighted.Web of Scienc
UBV(RI)C JHK observations of Hipparcos-selected nearby stars
We present homogeneous, standardized UBV(RI)C photometry for over 700 nearby stars
selected on the basis of Hipparcos parallaxes. Additionally, we list JHK photometry for about
half of these stars, as well as L photometry for 86 of the brightest. A number of stars with
peculiar colours or anomalous locations in various colourâmagnitude diagrams are discussed.Web of Scienc
The effect of dust obscuration in RR Tel on optical and IR long-term photometry and Fe II emission lines
Infrared and optical photometric and spectroscopic observations of the
symbiotic nova RR Tel are used to study the effects and properties of dust in
symbiotic binaries containing a cool Mira component, as well as showing
"obscuration events" of increased absorption, which are typical for such Miras.
A set of photometric observations of the symbiotic nova RR Tel in different
wavelength bands - visual from 1949 to 2002 and near-infrared (JHKL) from 1975
to 2002 - are presented. The variability due to the normal Mira pulsation was
removed from the JHKL data, which were then compared with the AAVSO visual
light curve. The changes of the Fe II emission line fluxes during the 1996-2000
obscuration episode were studied in the optical spectra taken with the
Anglo-Australian telescope.
We discuss the three periods during which the Mira component was heavily
obscured by dust as observed in the different wavelength bands. A change in the
correlations of J with other infrared magnitudes was observed with the colour
becoming redder after JD2446000. Generally, J-K was comparable, while K-L was
larger than typical values for single Miras. A distance estimate of 2.5 kpc,
based on the IR data, is given. A larger flux decrease for the permitted than
for the forbidden Fe II lines, during the obscuration episode studied, has been
found. There is no evidence for other correlations with line properties, in
particular with wavelength, which suggests obscuration due to separate
optically thick clouds in the outer layers.Comment: 19 pages, 11 figures, 3 table
Further observations of Hipparcos red stars and standards for UBV(RI)C photometry
We present homogeneous and standardized UBV(RI)C JHK photometry for over 100 M stars
selected from an earlier paper on the basis of apparent photometric constancy. L photometry
has been obtained for stars brighter than about L = 6. Most of the stars have a substantial
number of UBV(RI)C observations and, it is hoped, will prove useful as red supplementary
standards. Additionally,we list JHK photometry for nearly 300 Hipparcos red stars not selected
as standards, as well as L photometry for the brightest stars.Web of Scienc
On the nature of the cool component of MWC 560
Context.MWC 560 (V694 Mon) is one of the most enigmatic symbiotic system with a very active accretion-powered hot component. Such activity can be supported only by a luminous asymptotic giant branch star, i.e. a Mira or SR variable, with a high mass-loss rate. It is also a very unusual jet source because the jet axis lies practically parallel to the line of sight. Aims. The aims of our study are the determination of the evolutionary status of the cool component of MWC 560. Methods. Our methods involve analysis of near-IR JHKL and optical light curves. Results. The cool component of MWC 560 pulsates with a period of âŒ340 days, and it is probably a red SR variable on the thermally pulsing AGB. The high mass-loss rate expected for such a star is sufficient to power the observed activity of the hot companion
A search for previously unrecognised metal-poor subdwarfs in the Hipparcos astrometric catalogue
We have identified 317 stars included in the Hipparcos astrometric catalogue
which have parallaxes measured to a precision of better than 15%, and whose
location in the (M_V, (B-V)_T) diagram implies a metallicity comparable to or
less than that of the intermediate-abundance globular cluster, M5. We have
undertaken an extensive literature search to locate Stromgren, Johnson/Cousins
and Walraven photometry for over 120 stars. In addition, we present new UBVRI
photometry of 201 of these candidate halo stars, together with similar data for
a further 14 known metal-poor subdwarfs. Those observations provide the first
extensive dataset of RI photometry of metal-poor, main-sequence stars with
well-determined trigonometric parallaxes. Finally, we have obtained
intermediate-resolution optical spectroscopy of 175 stars. We are able to
estimate abundances for 270 stars. The overwhelming majority have near-solar
abundance, with their inclusion in the present sample stemming from errors in
the colours listed in the Hipparcos catalogue. Only 44 stars show consistent
evidence of abundances below [Fe/H]= -1.0. Nine are additions to the small
sample of metal-poor subdwarfs with accurate photometry. We consider briefly
the implication of these results for cluster main-sequence fitting.Comment: to appear in Monthly Notices of the Royal Astronomical Society (some
tables appear out of order in the text
The mysterious eruption of V838 Mon
V838 Mon is marking one of the most mysterious stellar outbursts on record.
The spectral energy distribution of the progenitor resembles an under-luminous
F main sequence star (at V=15.6 mag), that erupted into a cool supergiant
following a complex and multi-maxima lightcurve (peaking at V=6.7 mag). The
outburst spectrum show BaII, LiI and lines of several s-elements, with wide
P-Cyg profiles and a moderate and retracing emission in the Balmer lines. A
light-echo discovered expanding around the object helped to constrain the
distance (d=790+/-30 pc), providing M_V=+4.45 in quiescence and M_V=-4.35 at
optical maximum (somewhat dependent on the still uncertain E(B-V)=0.5
reddening). The general outburst trend is toward lower temperatures and larger
luminosities, and continuing so at the time of writing. The object properties
conflict with a classification within already existing categories: the
progenitor was not on a post-AGB track and thus the similarities with the
born-again AGB stars FG Sge, V605 Aql and Sakurai's object are limited to the
cool giant spectrum at maximum; the cool spectrum, the moderate wind velocity
(500 km/sec and progressively reducing) and the monotonic decreasing of the low
ionization condition argues against a classical nova scenario. The closest
similarity is with a star that erupted into an M-type supergiant discovered in
M31 by Rich et al. (1989), that became however much brighter by peaking at
M_V=-9.95, and with V4332 Sgr that too erupted into an M-type giant (Martini et
al. 1999) and that attained a lower luminosity, closer to that of V838 Mon.
M31-RedVar, V4332 Sgr and V838 Mon could be manifestations of the same and new
class of astronomical objects.Comment: A&A, in pres
HST and VLT observations of the Symbiotic Star Hen 2-147
We investigate the dynamics of the nebula around the symbiotic star Hen
2-147, determine its expansion parallax, and compare it with the distance
obtained via the Period-Luminosity relation for its Mira variable. The geometry
of the nebula is found to be that of a knotty annulus of ionized gas inclined
to the plane of sky and expanding with a velocity of ~90 km/s. A
straightforward application of the expansion parallax method provides a
distance of 1.5+-0.4 kpc, which is a factor of two lower than the distance of
3.0+-0.4 kpc obtained from the Period-Luminosity relationship for the Mira
(which has a pulsation period of 373 days). The discrepancy is removed if,
instead of expanding matter, we are observing the expansion of a shock front in
the plane of the sky. This shock interpretation is further supported by the
broadening of the nebular emission lines.Comment: Accepted for publication in A&A; 16 pages, 13 figure
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