431 research outputs found
The First Empirical Mass Loss Law for Population II Giants
Using the Spitzer IRAC camera we have obtained mid-IR photometry of the red
giant branch stars in the Galactic globular cluster 47 Tuc. About 100 stars
show an excess of mid-infrared light above that expected from their
photospheric emission. This is plausibly due to dust formation in mass flowing
from these stars. This mass loss extends down to the level of the horizontal
branch and increases with luminosity. The mass loss is episodic, occurring in
only a fraction of stars at a given luminosity. Using a simple model and our
observations we derive mass loss rates for these stars. Finally, we obtain the
first empirical mass loss formula calibrated with observations of Population II
stars. The dependence on luminosity of our mass loss rate is considerably
shallower than the widely used Reimers Law. The results presented here are the
first from our Spitzer survey of a carefully chosen sample of 17 Galactic
Globular Clusters, spanning the entire metallicity range from about one
hundredth up to almost solar
HST - WFPC2 photometry of the globular cluster ngc 288: binary systems, blue stragglers and very blue stars
We report on new WFPC2 observations of the globular cluster NGC 288, focusing
our attention on peculiar stars. A very pronounced binary sequence, paralleling
the ordinary Main Sequence (MS) is clearly observed in the Color Magnitude
Diagram (CMD) and a huge relative fraction of Blue Straggler Stars is measured.
The dataset offers the opportunity of studying the evolution of a large
population of binaries (and binary evolution by-products) in a low density
environment, where the evolution of such systems is not dominated by collisions
and encounters. Three (very) Extreme Horizontal Branch Stars have been found,
all lying outside of the cluster core.Comment: 6 pages, 3 figures, in press in the chemical evolution of the Milky
Way: stars versus clusters, F. Matteucci and F. Giovannelli eds, Kluwe
BVI Photometry and the Luminosity Function of the Globular Cluster M92
We present new BVI ground-based photometry and VI space-based photometry for
the globular cluster M92 (NGC 6341) and examine luminosity functions in B, V,
and I containing over 50,000 stars ranging from the tip of the red giant branch
to several magnitudes below the main sequence turn off. Once corrected for
completeness, the observed luminosity functions agree very well with
theoretical models and do not show stellar excesses in any region of the
luminosity function. Using reduced chi squared fitting, the new M92 luminosity
function is shown to be an excellent match to the previously published
luminosity function for M30. These points combine to establish that the
"subgiant excess" found in previously published luminosity functions of
Galactic globular clusters are due to deficiencies in the stellar models used
at that time. Using up to date stellar models results in good agreement between
observations and theory.
Several statistical methods are presented to best determine the age of M92.
These methods prove to be insensitive to the exact choice of metallicity within
the published range. Using [Fe/H]=-2.17 to match recent studies we find an age
of 14.2 plus or minus 1.2 Gyr for the cluster.Comment: 22 pages, 13 figures, 3 tables, accepted for publication in A
Different Characteristics of the Bright Branches of the Globular Clusters M3 and M13
We carried out wide-field BVI CCD photometric observations of the GCs M3 and
M13 using the BOAO 1.8 m telescope equipped with a 2K CCD. We present CMDs of
M3 and M13. We have found AGB bumps at V = 14.85 for M3 at V = 14.25 for M13.
It is found that AGB stars in M3 are more concentrated near the bump, while
those in M13 are scattered along the AGB sequence. We identified the RGB bump
of M3 at V = 15.50 and that of M13 at V = 14.80. We have estimated the ratios R
and R2 for M3 and M13 and found that of R for M3 is larger than that for M13
while R2's for M3 and M13 are similar when only normal HB stars are used in R
and R2 for M13. However, we found that R's for M3 and M13 are similar while R2
for M3 is larger than that for M13 when all the HB stars are included in R and
R2 for M13. We have compared the observed RGB LFs of M3 and M13 with the
theoretical RGB LF of Bergbusch & VandenBerg at the same radial distances from
the cluster centers as used in R and R2 for M3 and M13. We found "extra stars"
belonging to M13 in the comparison of the observed RGB LF of M13 and the
theoretical RGB LF of Bergbusch & VandenBerg. In the original definition of R
of Buzzoni et al., N(HB) corresponds to the lifetime of HB stars in the RR
Lyrae instability strip at log T_eff = 3.85. So, the smaller R value resulting
for M13 compared with that for M3 in the case where only normal HB stars are
included in R and R2 for M13 may be partially caused by "extra stars", and the
similar R's for M3 and M13 in the case where the all HB stars are included in R
and R2 for M13 may be caused by "extra stars" in the upper RGB of M13. If
"extra stars" in the upper RGB of M13 are caused by an effective "deep mixing"
these facts support the contention that an effective "deep mixing" could lead
to different HB morphologies between M3 and M13 and subsequent sequences.Comment: 24 pages, 7 figures, to be published in the A
The Star Formation History of the Carina Dwarf Galaxy
We have analyzed deep B and V photometry of the Carina dwarf spheroidal
reaching below the old main-sequence turnoff to about V = 25. Using simulated
color-magnitude diagrams to model a range of star formation scenarios, we have
extracted a detailed, global star formation history. Carina experienced three
significant episodes of star formation at about 15 Gyr, 7 Gyr, and 3 Gyr.
Contrary to the generic picture of galaxy evolution, however, the bulk of star
formation, at least 50%, occured during the episode 7 Gyr ago, which may have
lasted as long as 2 Gyr. For unknown reasons, Carina formed only 10-20% of its
stars at an ancient epoch and then remained quiescent for more than 4 Gyr. The
remainder (~30%) formed relatively recently, only 3 Gyr ago. Interest in the
local population of dwarf galaxies has increased lately due to their potential
importance in the understanding of faint galaxy counts. We surmise that objects
like Carina, which exhibits the most extreme episodic behavior of any of the
dwarf spheroidal companions to the Galaxy, are capable of contributing to the
observed excess of blue galaxies at B = 24 only if the star formation occurred
instantaneously.Comment: 23 pages of text, 20 figures, 8 tables. AJ, in pres
Influencing Factors in Autotransplantation of Teeth with Open Apex: A Review of the Literature
Dental autotransplantation is the process by which a tooth located in its natural socket is extracted and relocated to another socket in which the tooth is missing or has been extracted due to various reasons such as trauma, extensive caries or periapical pathology, among other reasons. This proposed technique offers a more conservative alternative for patients in comparison with prosthetic or implant techniques, especially in young patients where implants are contraindicated until their maxillary bone systemâs growth ends. Thus, the objective of this review was to present a qualitative synthesis of the risk factors that influence the results of open apex dental autotransplantation in humans. After confirming that there are various factors that influence dental autotransplantation, it was concluded that the extra-alveolar time of the donor tooth and the periodontal damage of the root of the donor tooth are the factors of greatest interest in the literature, both closely linked to the use of 3D replication of the transplanted toot
An HST/WFPC2 survey of bright young clusters in M31. I. VdB0, a massive star cluster seen at t â 25 Myr
Aims. We introduce our imaging survey of possible young massive globular clusters in M31 performed with the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). We obtained shallow (to B ~ 25) photometry of individual stars in 20 candidate clusters. We present here details of the data reduction pipeline that is being applied to all the survey data and describe its application to the brightest among our targets, van den Bergh 0 (VdB0), taken as a test case.
Methods. Point spread function fitting photometry of individual stars was obtained for all the WFPC2 images of VdB0 and the completeness of the final samples was estimated using an extensive set of artificial stars experiments. The reddening, the age and the metallicity of the cluster were estimated by comparing the observed color magnitude diagram (CMD) with theoretical isochrones. Structural parameters were obtained from model-fitting to the intensity profiles measured within circular apertures on the WFPC2 images.
Results. Under the most conservative assumptions, the stellar mass of VdB0 is M> 2.4 x 10^4 M_â , but our best estimates lie in the range â4-9 x 10^4 M_â. The CMD of VdB0 is best reproduced by models having solar metallicity and age â25 Myr. Ages less than â12 Myr and greater than â60 Myr are clearly ruled out by the available data. The cluster has a remarkable number of red super giants (âł18) and a CMD very similar to Large Magellanic Cloud clusters usually classified as young globulars such as NGC 1850, for example.
Conclusions. VdB0 is significantly brighter (âł1 mag) than Galactic open clusters of similar age. Its present-day mass and half-light radius ((r_h = 7.4 pc) are more typical of faint globular clusters than of open clusters. However, given its position within the disk of M31, it is expected to be destroyed by dynamical effects, in particular by encounters with giant molecular clouds, within the next ~4 Gyr
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
Calculation of biophysical indicators through the automatic processing of satellite images
In recent years, remote sensing has emerged as one of the most useful tools in agronomy. A series of biophysical indicators can be derived from satellite images and used as inputs for decision support systems in irrigation management, crop planning or determination of crop yields, thus achieving a better management of resources. An automated system implemented under the IDEaRM services provides these indicators on a daily rate to support in decision-making.This work has been done through the project âTelerieg â Remote sensing use for irrigation practice recommendation and monitoring in the SUDOE spaceâ financed by Programme (SUDOE), which supports regional development through European Regional Development Fund (ERDF) co-financing of transnational projects
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