1,617 research outputs found
On the observational properties of He-burning stars: some clues on the tilt of the HB in metal rich clusters
We investigate the predicted Color-Magnitude distribution of metal-rich
Horizontal Branch (HB) stars, discussing selected theoretical models computed
under various assumptions about the star metallicity and the efficiency of
super-adiabatic convection. We find that canonical Zero Age Horizontal Branches
with metallicity larger or of the order of Z=0.002 should be all affected by a
tilt, by an amount which increases when the metallicity is increased and/or the
mixing length is decreased, reaching a tilt of 0.2 mag in the
case of solar metallicity when a mixing length value =1.6 is assumed
( is the magnitude difference between the top of the blue HB and the
fainter magnitude reached by the red HB). Uncertainties in the luminosity of
the red HB due to uncertainty in the mixing length value are discussed. We
finally discuss the much larger tilt observed in the clusters NGC 6441 and NGC
6388, reporting additional evidence against suggested non-canonical
evolutionary scenarios. Numerical experiments show that differential reddening
could produce such sloped HBs. Further, HST-PC imaging of NGC 6441 gives clear
indications about the occurrence of differential reddening across the cluster.
However, the same imaging shows that the observed slope of the red HB {\em is
not} an artifact of differential reddening. We finally show that sloping red
HBs in metal rich clusters are a common occurrence not necessarily correlated
with the appearance of extended blue HB.Comment: 14 pages, 9 figures, Accepted by Ap
The blue sky of GJ3470b: the atmosphere of a low-mass planet unveiled by ground-based photometry
GJ3470b is a rare example of a "hot Uranus" transiting exoplanet orbiting a
nearby M1.5 dwarf. It is of crucial interest for atmospheric studies because it
is one of the most inflated low-mass planets known, bridging the boundary
between "super-Earths" and Neptunian planets. We present two new ground-based
light curves of GJ3470b gathered by the LBC camera at the Large Binocular
Telescope. Simultaneous photometry in the ultraviolet (lambda_c = 357.5 nm) and
optical infrared (lambda_c = 963.5 nm) allowed us to detect a significant
change of the effective radius of GJ3470b as a function of wavelength. This can
be interpreted as a signature of scattering processes occurring in the
planetary atmosphere, which should be cloud-free and with a low mean molecular
weight. The unprecedented accuracy of our measurements demonstrates that the
photometric detection of Earth-sized planets around M dwarfs is achievable
using 8-10m size ground-based telescopes. We provide updated planetary
parameters, and a greatly improved orbital ephemeris for any forthcoming study
of this planet.Comment: 8 pages, 6 figures, 1 table; accepted for publication in A&
Deep HST-WFPC2 photometry of NGC 288. II. The Main Sequence Luminosity Function
The Main Sequence Luminosity Function (LF) of the Galactic globular cluster
NGC 288 has been obtained using deep WFPC2 photometry. We have employed a new
method to correct for completeness and fully account for bin-to-bin migration
due to blending and/or observational scatter. The effect of the presence of
binary systems in the final LF is quantified and is found to be negligible.
There is a strong indication of the mass segregation of unevolved single stars
and clear signs of a depletion of low mass stars in NGC 288 with respect to
other clusters. The results are in good agreement with the prediction of
theoretical models of the dynamical evolution of NGC 288 that take into account
the extreme orbital properties of this cluster.Comment: 16 pages, 6 .ps figures. Low resolution version of fig. 1; full
resolution figure soon available at http://www.bo.astro.it/bap/BAPhome.html
l. Latex. emulateapj5.sty macro included. Accepted for publication by The
Astronomical Journa
Absolute proper motion of the Galactic open cluster M67
We derived the absolute proper motion (PM) of the old, solar-metallicity
Galactic open cluster M67 using observations collected with CFHT (1997) and
with LBT (2007). About 50 galaxies with relatively sharp nuclei allow us to
determine the absolute PM of the cluster. We find (mu_alpha
cos(delta),mu_delta)_J2000.0 = (-9.6+/-1.1,-3.7+/-0.8) mas/yr. By adopting a
line-of-sight velocity of 33.8+/-0.2 km/s, and assuming a distance of 815+/-50
pc, we explore the influence of the Galactic potential, with and without the
bar and/or spiral arms, on the galactic orbit of the cluster.Comment: 7 pages, 5 figures, and 3 tables. Published in Astronomy and
Astrophysics, Volume 513, id.A51
Radial extent of the SGB in NGC 1851
Recent HST-ACS observations revealed the presence of a double subgiant branch
(SGB) in the core of the Galactic globular cluster NGC 1851. This peculiarity
was tentatively explained by the presence of a second population with either an
age difference of about 1 Gyr, or a higher C+N+O abundance, probably due to
pollution by the first generation of stars.
In the present Letter, we analyze VLT-FORS V,I images, covering 12.7x12.7
arcmin, in the southwest quadrant of the cluster, allowing us to probe the
extent of the double SGB from ~1.4 to ~13 arcmin from the cluster center. Our
study reveals, for the first time, that the "peculiar" population is the one
associated to the fainter SGB. Indeed, while the percentage of stars in this
sequence is about 45% in the cluster core (as previously found on the basis of
HST-ACS data), we find that it drops sharply, to a level consistent with zero
in our data, at ~2.4 arcmin from the cluster center, where the brighter SGB, in
our sample, still contains ~100 stars. Implications for the proposed scenarios
are discussed.Comment: Revised text, 1 new figure. No major chang
Photometry Results for the Globular Clusters M10 and M12: Extinction Maps, Color-Magnitude Diagrams, and Variable Star Candidates
We report on photometry results of the equatorial globular clusters (GCs) M10
and M12. These two clusters are part of our sample of GCs which we are probing
for the existence of photometrically varying eclipsing binary stars. During the
search for binaries in M10 and M12, we discovered the signature of differential
reddening across the fields of the clusters. The effect is stronger for M10
than for M12. Using our previously described dereddening technique, we create
differential extinction maps for the clusters which dramatically improve the
appearance of the color-magnitude diagrams (CMDs). Comparison of our maps with
the dust emissivity maps of Schlegel, Finkbeiner, & Davis (SFD) shows good
agreement in terms of spatial extinction features. Several methods of adding an
E_{V-I} zero point to our differential maps are presented of which isochrone
fitting proved to be the most successful. Our E_{V-I} values fall within the
range of widely varying literature values. More specifically, our reddening
zero point estimate for M12 agrees well with the SFD estimate, whereas the one
for M10 falls below the SFD value. Our search for variable stars in the
clusters produced a total of five variables: three in M10 and two in M12. The
M10 variables include a binary system of the W Ursa Majoris (W UMa) type, a
background RR Lyrae star, and an SX Phoenicis pulsator, none of which is
physically associated with M10. M12's variables are two W UMa binaries, one of
which is most likely a member of the cluster. We present the phased photometry
lightcurves for the variable stars, estimate their distances, and show their
locations in the fields and the CMDs of the GCs.Comment: 22 pages, 21 figures, to be published in AJ October 2002. For a
higher-resolution version of this paper, please visit
http://www.astro.lsa.umich.edu/~kaspar/M10_M12_photometry.ps.gz (gzipped
postscript) or http://www.astro.lsa.umich.edu/~kaspar/M10_M12_photometry.pdf
(pdf file
Discovery of Carbon/Oxygen depleted Blue Straggler Stars in 47 Tucanae: the chemical signature of a mass-transfer formation process
We use high-resolution spectra obtained with the ESO Very Large Telescope to
measure surface abundance patterns of 43 Blue Stragglers stars (BSS) in 47 Tuc.
We discovered that a sub-population of BSS shows a significant depletion of
Carbon and Oxygen with respect to the dominant population. This evidence would
suggest the presence of CNO burning products on the BSS surface coming from a
deeply peeled parent star, as expected in the case of mass-transfer process.
This is the first detection of a chemical signature clearly pointing to a
specific BSS formation process in a globular cluster.Comment: Published on 2006, August 10, in ApJ 647, L5
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