20,275 research outputs found
SACY - a Search for Associations Containing Young stars
The scientific goal of the SACY (Search for Associations Containing
Young-stars) was to identify possible associations of stars younger than the
Pleiades Association among optical counterparts of the ROSAT X-ray bright
sources. High-resolution spectra for possible optical counterparts later than
G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to
assess both the youth and the spatial motion of each target. More than 1000
ROSAT sources were observed, covering a large area in the Southern Hemisphere.
The newly identified young stars present a patchy distribution in UVW and XYZ,
revealing the existence of huge nearby young associations. Here we present the
associations identified in this survey.Comment: 8 pages, 2 figures, to appear in the Proceedings of Open Issues in
Local Formation and Early Stellar Evolution, Ouro Preto, Brazi
GHASP: an H{\alpha} kinematic survey of spiral and irregular galaxies -- IX. The NIR, stellar and baryonic Tully-Fisher relations
We studied, for the first time, the near infrared, stellar and baryonic
Tully-Fisher relations for a sample of field galaxies taken from an homogeneous
Fabry-Perot sample of galaxies (the GHASP survey). The main advantage of GHASP
over other samples is that maximum rotational velocities were estimated from 2D
velocity fields, avoiding assumptions about the inclination and position angle
of the galaxies. By combining these data with 2MASS photometry, optical colors,
HI masses and different mass-to-light ratio estimators, we found a slope of
4.48\pm0.38 and 3.64\pm0.28 for the stellar and baryonic Tully-Fisher relation,
respectively. We found that these values do not change significantly when
different mass-to-light ratios recipes were used. We also point out, for the
first time, that rising rotation curves as well as asymmetric rotation curves
show a larger dispersion in the Tully-Fisher relation than flat ones or than
symmetric ones. Using the baryonic mass and the optical radius of galaxies, we
found that the surface baryonic mass density is almost constant for all the
galaxies of this sample. In this study we also emphasize the presence of a
break in the NIR Tully-Fisher relation at M(H,K)\sim-20 and we confirm that
late-type galaxies present higher total-to-baryonic mass ratios than early-type
spirals, suggesting that supernova feedback is actually an important issue in
late-type spirals. Due to the well defined sample selection criteria and the
homogeneity of the data analysis, the Tully-Fisher relation for GHASP galaxies
can be used as a reference for the study of this relation in other environments
and at higher redshifts.Comment: 16 pages, 6 figures. Accepted for publication in MNRA
Star formation in low density HI gas around the Elliptical Galaxy NGC2865
Interacting galaxies surrounded by HI tidal debris are ideal sites for the
study of young clusters and tidal galaxy formation. The process that triggers
star formation in the low-density environments outside galaxies is still an
open question. New clusters and galaxies of tidal origin are expected to have
high metallicities for their luminosities. Spectroscopy of such objects is,
however, at the limit of what can be done with existing 8-10m class telescopes,
which has prevented statistical studies of these objects. NGC2865 is an
UV-bright merging elliptical galaxy with shells and extended HI tails. The
regions observed in this work were previously detected using multi-slit imaging
spectroscopy. We obtain new multislit spectroscopy of six young star-forming
regions around NGC2865, to determine their redshifts and metallicities. The six
emission-line regions are located 16-40 kpc from NGC2865 and they have similar
redshifts. They have ages of ~10Myears and an average metallicity of
12+log(O/H) ~ 8.6, suggesting a tidal origin for the regions. It is noted that
they coincide with an extended HI tail, which has projected density of N
< 10 cm, and displays a low surface brightness counterpart. These
regions may represent the youngest of the three populations of star clusters
already identified in NGC2865. The high, nearly-solar, oxygen abundances found
for the six regions in the vicinity of NGC2865 suggest that they were formed by
pre-enriched material from the parent galaxy, from gas removed during the last
major merger. Given the mass and the location of the HII regions, we can
speculate that these young star-forming regions are potential precursors of
globular clusters that will be part of the halo of NGC2865 in the future. Our
result supports the use of the multi-slit imaging spectroscopy as a useful tool
for finding nearly-formed stellar systems around galaxies.Comment: 7 pages, 2 figures accepted in A&
Search for Associations Containing Young stars (SACY): Chemical tagging IC 2391 & the Argus association
We explore the possible connection between the open cluster IC 2391 and the
unbound Argus association identified by the SACY survey. In addition to common
kinematics and ages between these two systems, here we explore their chemical
abundance patterns to confirm if the two substructures shared a common origin.
We carry out a homogenous high-resolution elemental abundance study of eight
confirmed members of IC 2391 as well as six members of the Argus association
using UVES spectra. We derive spectroscopic stellar parameters and abundances
for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba.
All stars in the open cluster and Argus association were found to share
similar abundances with the scatter well within the uncertainties, where [Fe/H]
= -0.04 +/-0.03 for cluster stars and [Fe/H] = -0.06 +/-0.05 for Argus stars.
Effects of over-ionisation/excitation were seen for stars cooler than roughly
5200K as previously noted in the literature. Also, enhanced Ba abundances of
around 0.6 dex were observed in both systems. The common ages, kinematics and
chemical abundances strongly support that the Argus association stars
originated from the open cluster IC 2391. Simple modeling of this system find
this dissolution to be consistent with two-body interactions.Comment: 17 pages, 7 figs, accepted for publication in MNRA
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