132 research outputs found
A Photometric Study of the Outer Halo Globular Cluster NGC 5824
Multi-wavelength CCD photometry over 21 years has been used to produce deep
color-magnitude diagrams together with light curves for the variables in the
Galactic globular cluster NGC 5824. Twenty-one new cluster RR Lyrae stars are
identified, bringing the total to 47, of which 42 have reliable periods
determined for the first time. The color-magnitude diagram is matched using
BaSTI isochrones with age of ~Gyr. and reddening is found to be ; using the period-Wesenheit relation in two colors the distance
modulus is corresponding to a distance of 30.9 Kpc.
The observations show no signs of populations that are significantly younger
than the ~Gyr stars. The width of the red giant branch does not allow for a
spread in [Fe/H] greater than dex, and there is no photometric
evidence for widened or parallel sequences. The pseudo-color
magnitude diagram shows a bifurcation of the red giant branch that by analogy
with other clusters is interpreted as being due to differing spectral
signatures of the first (75\%) and second (25\%) generations of stars whose age
difference is close enough that main sequence turnoffs in the color-magnitude
diagram are unresolved. The cluster main sequence is visible against the
background out to a radial distance of arcmin. We conclude that NGC
5824 appears to be a classical Oosterhoff Type II globular cluster, without
overt signs of being a remnant of a now-disrupted dwarf galaxy.Comment: 26 pages, 15 figures, 4 tables, accepted for publication in
Astronomical Journa
The distance to the LMC cluster Reticulum from the K-band Period-Luminosity-Metallicity relation of RR Lyrae stars
We present new and accurate Near-Infrared J and Ks-band data of the Large
Magellanic Cloud cluster Reticulum. Data were collected with SOFI available at
NTT and covering an area of approximately (5 x 5) arcmin^2 around the center of
the cluster. Current data allowed us to derive accurate mean K-band magnitudes
for 21 fundamental and 9 first overtone RR Lyrae stars. On the basis of the
semi-empirical K-band Period-Luminosity-Metallicity relation we have recently
derived, we find that the absolute distance to this cluster is 18.52 +- 0.005
(random) +- 0.117 (systematic). Note that the current error budget is dominated
by systematic uncertainty affecting the absolute zero-point calibration and the
metallicity scale.Comment: 14 pages, 2 figures, ApJ accepted. Full resolution figure 1 on
request ([email protected]
Variable Stars in Local Group Galaxies. IV. RR Lyrae stars in the central regions of the low-density galaxy Crater II
We present a search and analysis of variable stars in the recently discovered
Crater~II dwarf galaxy. Based on , , data collected with the Isaac
Newton Telescope (FoV0.44 square degrees) we detected 37 variable stars,
of which 34 are bone-fide RR Lyrae stars of Crater~II (28 RRab, 4 RRc, 2 RRd).
We applied the metal-independent (, ) Period--Wesenheit relation and
derived a true distance modulus ( = 20.300.08 mag (=0.16
mag). Individual metallicities for RR Lyrae stars were derived by inversion of
the predicted -band Period-Luminosity relation. We find a mean metallicity
of [Fe/H]=-1.64 and a standard deviation of =0.21 dex,
compatible with either negligible or vanishing intrinsic metallicity
dispersion. The analysis of the Colour-Magnitude Diagram reveals a stark
paucity of blue horizontal branch stars, at odds with other Galactic dwarfs,
and globular clusters with similar metal abundances.Comment: 14 pages, 8 figures, accepted for publications on MNRAS. Time series
photometry is available in the manuscript source ta
Constraints on the Formation of the Globular Cluster IC 4499 from Multi-Wavelength Photometry
We present new multiband photometry for the Galactic globular cluster IC 4499
extending well past the main sequence turn-off in the U, B, V, R, I, and DDO51
bands. This photometry is used to determine that IC4499 has an age of 12 pm 1
Gyr and a cluster reddening of E(B-V) = 0.22 pm 0.02. Hence, IC 4499 is coeval
with the majority of Galactic GCs, in contrast to suggestions of a younger age.
The density profile of the cluster is observed to not flatten out to at least
r~800 arcsec, implying that either the tidal radius of this cluster is larger
than previously estimated, or that IC 4499 is surrounded by a halo. Unlike the
situation in some other, more massive, globular clusters, no anomalous color
spreads in the UV are detected among the red giant branch stars. The small
uncertainties in our photometry should allow the detection of such signatures
apparently associated with variations of light elements within the cluster,
suggesting that IC 4499 consists of a single stellar population.Comment: accepted to MNRA
TIC 43152097. The first eclipsing binary in NGC 2232
We report the discovery of a low-mass totally eclipsing system in the young
(age28 Myr) open cluster NGC2232, during a scrutiny of their TESS light
curves. The follow-up study of this detached system, TIC 43152097, is based on
photometry and high-resolution spectra from the literature and purposely
collected. The radial velocity of the center of mass, as well as the
photospheric lithium abundance of the binary components, confirm its membership
to NGC2232. By analyzing the existing photometric and spectroscopic data, we
obtain orbital elements and fundamental stellar parameters for the two stars.
The primary component of TIC 43152097 is a late F-type dwarf (Teff = 6070 K),
while the lower-mass secondary results to be a late K-type star (Teff = 4130 K)
that is still in the pre-main-sequence phase. The precise measurements of
radii, masses, and effective temperatures, enabled by the simultaneous solution
of light and radial velocity curves, indicate radius inflation for the K-type
component, which turns out to be 7-11 % larger than predicted by standard
evolutionary models. More sophisticated models incorporating both inhibition of
convective energy transport caused by sub-photospheric magnetic fields and the
effects by cool starspots covering a substantial fraction of the stellar
surface (30-60 %) allow reproducing the position of the secondary component in
the Hertzsprung-Russell and Mass-Radius diagrams.Comment: 11 pages, 15 figures; accepted for publication in Astronomy &
Astrophysic
The RR Lyrae distance scale from near-infrared photometry: current results
We present new observational results on the RR Lyrae K-band Period-Luminosity
relation (PLK). Data on the Galactic globular clusters NGC 3201 and NGC 4590
(M68), and on the Large Magellanic Cloud cluster Reticulum are shown. We
compare the observed slopes of the PLK relations for these three clusters with
those predicted by pulsational and evolutionary models, finding a fair
agreement. Trusting on this finding we decided to adopt these theoretical
calibrations to estimate the distance to the target clusters,finding a good
agreement with optical-based RR Lyrae distances, but with a smaller formal
scatter.Comment: Proceedings of the Stellar Pulsation and Evolution meeting, Rome,
June 200
VLT FORS-1 observations of NGC 6397: Evidence for mass segregation
We present (V,V-I) VLT-FORS1 observations of the Galactic Globular Cluster
NGC 6397. We derive accurate color--magnitude diagrams and luminosity functions
(LFs) of the cluster Main Sequence (MS) for two fields extending from a region
near the centre of the cluster out to ~ 10 arcmin. The photometry of these
fields produces a narrow MS extending down to V ~ 27, much deeper than any
previous ground based study on this system and comparable to previous HST
photometry. The V, V-I CMD also shows a deep white dwarf cooling sequence
locus, contaminated by many field stars and spurious objects. We concentrate
the present work on the analysis of the MSLFs derived for two annuli at
different radial distance from the center of the cluster. Evidence of a
clear-cut correlation between the slope of the observed LFs before reaching the
turn-over, and the radial position of the observed fields inside the cluster
area is found. We find that the LFs become flatter with decreasing radius (x ~
0.15 for 1'< R1 < 5.5'; x ~ 0.24 for 5.5'< R2 <9.8'; core radius, rc = 0.05'),
a trend that is consistent with the interpretation of NGC 6397 as a dynamically
relaxed system. This trend is also evident in the mass function.Comment: 11 pages; 15 figures; accepted for publication on Astronomy and
Astrophysic
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