704 research outputs found
The Araucaria Project. The Distance to the Small Magellanic Cloud from Near-Infrared Photometry of RR Lyrae Variables
We have obtained deep infrared J and K band observations of nine 4.9x4.9
arcmin fields in the Small Magellanic Cloud (SMC) with the ESO New Technology
Telescope equipped with the SOFI infrared camera. In these fields, 34 RR Lyrae
stars catalogued by the OGLE collaboration were identified. Using different
theoretical and empirical calibrations of the infrared
period-luminosity-metallicity relation, we find consistent SMC distance moduli,
and find a best true distance modulus to the SMC of 18.97 +/- 0.03
(statistical) +/- 0.12 (systematic) mag which agrees well with most independent
distance determinations to this galaxy, and puts the SMC 0.39 mag more distant
than the LMC for which our group has recently derived, from the same technique,
a distance of 18.58 mag.Comment: AJ submitted and accepte
The Araucaria Project. Population effects on the V and I band magnitudes of red clump stars
We present measurements of the V and I band magnitudes of red clump stars in
15 nearby galaxies obtained from recently published homogenous HST photometry.
Supplementing these results with similar data for another 8 galaxies available
in the literature the populational effects on the V and I band magnitudes of
red clump stars were investigated. Comparing red clump magnitudes with the
I-band magnitude of the TRGB in a total sample of 23 galaxies possessing very
different environments we demonstrate that population effects strongly affect
both the V and I band magnitude of red clump stars in a complex way. Our
empirical results basically confirm the theoretical results of Girardi and
Salaris, and show that optical (VI) photometry of red clump stars is not an
accurate method for the determination of distances to nearby galaxies at the
present moment, as long as the population effects are not better calibrated,
both empirically and theoretically. Near infrared photometry is a much better
way to measure galaxy distances with red clump stars given its smaller
sensitivity to population effects.Comment: AJ in pres
A new LMC K-band distance from precision measurements of nearby red clump stars
High-precision (sigma < 0.01) new JHK observations of 226 of the brightest
and nearest red clump stars in the solar neighbourhood are used to determine
distance moduli for the LMC. The resulting K- and H-band values of 18.47\pm0.02
and 18.49\pm0.06 imply that any correction to the K-band Cepheid PL relation
due to metallicity differences between Cepheids in the LMC and in the solar
neighborhood must be quite small.Comment: 7 pages, 4 figure
The Araucaria Project. First Cepheid Distance to the Sculptor Group Galaxy NGC 7793 from Variables discovered in a Wide-Field Imaging Survey
We have detected, for the first time, Cepheid variables in the Sculptor Group
spiral galaxy NGC 7793. From wide-field images obtained in the optical V and I
bands on 56 nights in 2003-2005, we have discovered 17 long-period (24-62 days)
Cepheids whose periods and mean magnitudes define tight period-luminosity
relations. We use the (V-I) Wesenheit index to determine a reddening-free true
distance modulus to NGC 7793 of 27.68 +- 0.05 mag (internal error) +- 0.08 mag
(systematic error). The comparison of the reddened distance moduli in V and I
with the one derived from the Wesenheit magnitude indicates that the Cepheids
in NGC 7793 are affected by an average total reddening of E(B-V)=0.08 mag, 0.06
of which is produced inside the host galaxy. As in the earlier Cepheid studies
of the Araucaria Project, the reported distance is tied to an assumed LMC
distance modulus of 18.50. The quoted systematic uncertainty takes into account
effects like blending and possible inhomogeneous filling of the Cepheid
instability strip on the derived distance. The reported distance value does not
depend on the (unknown) metallicity of the Cepheids according to recent
theoretical and empirical results. Our Cepheid distance is shorter, but within
the errors consistent with the distance to NGC 7793 determined earlier with the
TRGB and Tully-Fisher methods. The NGC 7793 distance of 3.4 Mpc is almost
identical to the one our project had found from Cepheid variables for NGC 247,
another spiral member of the Sculptor Group located close to NGC 7793 on the
sky. Two other conspicuous spiral galaxies in the Sculptor Group, NGC 55 and
NGC 300, are much nearer (1.9 Mpc), confirming the picture of a very elongated
structure of the Sculptor Group in the line of sight put forward by Jerjen et
al. and others.Comment: AJ in pres
The Araucaria Project. The Distance to the Sculptor dwarf spheroidal galaxy from infrared photometry of RR Lyrae stars
We have obtained single-phase near-infrared magnitudes in the J and K bands
for a sample of 78 RR Lyrae stars in the Sculptor dSph galaxy. Applying
different theoretical and empirical calibrations of the
period-luminosity-metallicity relation for RR Lyrae stars in the infrared, we
find consistent results and obtain a true, reddening-corrected distance modulus
of 19.67 0.02 (statistical) 0.12 (systematic) mag for Sculptor from
our data. This distance value is consistent with the value of 19.68 0.08
mag which we obtain from earlier V-band data of RR Lyrae stars in Sculptor, and
the V magnitude-metallicity calibration of Sandage (1993). It is also in a very
good agreement with the results obtain by Rizzi (2002) based on tip of the red
giant branch (TRGB, 19.64 0.08 mag) and horizontal branch (HB, 19.66
0.15 mag).Comment: AJ in pres
The Araucaria Project. The Distance to the Sculptor Galaxy NGC 247 from Near-Infrared Photometry of Cepheid Variables
We have obtained deep near-infrared images in J and K filters of four fields
in the Sculptor Group spiral galaxy NGC 247 with the ESO VLT and ISAAC camera.
For a sample of ten Cepheids in these fields, previously discovered by
Garc{\'i}a-Varela et al. from optical wide-field images, we have determined
mean J and K magnitudes and have constructed the period-luminosity (PL)
relations in these bands. Using the near-infrared PL relations together with
those in the optical V and I bands, we have determined a true distance modulus
for NGC 247 of 27.64 mag, with a random uncertainty of 2% and a systematic
uncertainty of 4% which is dominated by the effect of unresolved stars on
the Cepheid photometry. The mean reddening affecting the NGC 247 Cepheids of
E(B-V) = 0.18 0.02 mag is mostly produced in the host galaxy itself and
is significantly higher than what was found in the previous optical Cepheid
studies in NGC 247 of our own group, and Madore et al., leading to a 7%
decrease in the previous optical Cepheid distance. As in other studies of our
project, the distance modulus of NGC 247 we report is tied to an assumed LMC
distance modulus of 18.50. Comparison with other distance measurements to NGC
247 shows that the present IR-based Cepheid distance is the most accurate among
these determinations.
With a distance of 3.4 Mpc, NGC 247 is about 1.5 Mpc more distant than NGC 55
and NGC 300, two other Sculptor Group spirals analyzed before with the same
technique by our group.Comment: W. Gieren, G. Pietrzynski, I. Soszynski, O. Szewczyk, Bresolin F.,
Kudritzki, R.P., Urbajeja M., Jesper S., Minniti D., Garcia-Varela A.,. ApJ
in pres
Photometry of two unusual A supergiant systems in the Small Magellanic Cloud
We present multiwavelength broadband photometry and V, I time resolved
photometry for two variable bright stars in the SMC, OGLE004336.91-732637.7
(SMC-SC3) and OGLE004633.76-731204.3 (SMC-SC4). The light curves span 12 years
and show long-term periodicities (SMC-SC3) and modulated eclipses (SMC-SC4)
that are discussed in terms of wide-orbit intermediate mass interacting
binaries and associated envelopes. SMC-SC3 shows a primary period of 238.1 days
along with a complicated waveform suggesting ellipsoidal variablity influenced
by an eccentric orbit. This star also shows a secondary variability with an
unstable periodicity that has a mean value of 15.3 days. We suggest this could
be associated with nonradial pulsations.Comment: To be published in Publications of the Astronomical Society of the
Pacific (PASP)
The Araucaria Project. Infrared TRGB distances to the Carina and Fornax dwarf spheroidal galaxies
We present distance determinations for two Local Group dwarf spheroidal
galaxies, Carina and Fornax, based on the near-infrared magnitudes of the tip
of the red giant branch (TRGB). For Carina we derive true distance moduli of
20.09 and 20.13 mag in the J and K bands, respectively, while for Fornax the
same distance modulus of 20.84 mag was derived in both filters. The statistical
errors of these determinations are of order 0.03-0.04 mag, whereas the
systematic uncertainties on the distances are 0.12 mag in the J band and 0.14
mag in the K band. The distances obtained from the near-infrared TRGB method in
this paper agree very well with those obtained for these two galaxies from
optical calibrations of the TRGB method, their horizontal branches, RR Lyrae
variables, and the near-infrared magnitudes of their red clumps.Comment: Accepted to be published on A
Using Ultra Long Period Cepheids to Extend the Cosmic Distance Ladder to 100 Mpc and Beyond
We examine the properties of 17 long period (80-180 days) and very luminous
(median absolute magnitude of M_I= -7.93 and M_V= -7.03) Cepheids to see if
they can serve as an useful distance indicator. We find that these Ultra Long
Period (ULP) Cepheids have a relatively shallow Period-Luminosity (PL)
relation, so in fact they are more "standard candle"-like than classical
Cepheids. In the reddening-free Wesenheit index, the slope of the ULP PL
relation is ~10 times less steep than the standard PL relation for the SMC
Cepheids. The scatter of our sample about the W_I PL relation is 0.22 mag,
approaching that of classical Cepheids and Type Ia Supernovae. We expect this
scatter to decrease as bigger and more uniform samples of ULP Cepheids are
obtained. We also measure a non-zero period derivative for one ULP Cepheid (SMC
HV829) and use the result to probe evolutionary models and mass loss of massive
stars. ULP Cepheids main advantage over classical Cepheids is that they are
more luminous, and as such show great potential as stellar distance indicators
to galaxies up to 100 Mpc and beyond.Comment: Accepted for Publication in ApJ. 11 pages, 8 figure
A Catalogue of Be Stars in the Direction of the Galactic Bulge
Detailed studies of Be stars in environments with different metallicities
like the Magellanic Clouds or the Galactic bulge are necessary to understand
the formation and evolution mechanisms of the circumstellar disks. However, a
detailed study of Be stars in the direction of the bulge of our own galaxy has
not been performed until now. We report the first systematic search for Be star
candidates in the direction of the Galactic Bulge. We present the catalogue,
give a brief description of the stellar variability seen, and show some light
curve examples. We searched for stars matching specific criteria of magnitude,
color and variability in the I band. Our search was conducted on the 48 OGLE II
fields of the Galactic Bulge.This search has resulted in 29053 Be star
candidates, 198 of them showing periodic light variations. Nearly 1500 stars in
this final sample are almost certainly Be stars, providing an ideal sample for
spectroscopic multiobject follow-up studies.Comment: Accepted for publication in A &
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