3 research outputs found
Survey of the ISM in Early-Type Galaxies. IV. The Hot Dust Component
We present mid-IR photometric properties for a sample of 28 early-type
galaxies observed at 6.75, 9.63 and 15 um with the ISOCAM instrument on board
the ISO satellite. We find total mid-IR luminosities in the range 3-48x10^8
L_sun. The spectral energy distribution (SED) of the galaxies were derived
using the mid-IR data together with previously published UV, optical and
near-IR data. These SEDs clearly show a mid-IR emission coming from dust heated
at T ~ 260 K. Dust grains properties are inferred from the mid-IR colors. The
masses of the hot dust component are in the range 10-400 M_sun. The
relationship between the masses derived from mid-IR observations and those
derived from visual extinction are discussed. The possible common heating
source for the gas and dust is investigated through the correlations between Ha
and mid-IR luminosities.Comment: 10 pages, LaTeX (aa.cls), 11 figures (f. 2-4 are colour plates).
Accepted for publication in Astronomy & Astrophysic
Low-resolution spectroscopy of main sequence stars belonging to 12 Galactic globular clusters. I. CH and CN band strength variations
Globular clusters show abundance variations for light elements that are not
yet well understood. The preferred explanation involves a self-enrichment
scenario, with two subsequent generations of stars. Observations of main
sequence stars allow us to investigate the signature of this chemically
processed material without the complicating effects of internal mixing. Our
goal is to investigate the C-N anti-correlation with low-resolution
spectroscopy of 20-50 stars fainter than the first dredge-up in seven globular
clusters (NGC288, NGC1851, NGC5927, NGC6352, NGC6388, and Pal12) with different
properties. We complemented our observations with 47~Tuc archival data, with
four additional clusters from the literature (M15, M22, M55, NGC362), and with
additional literature data on NGC288. In this first paper, we measured the
strength of CN and CH band indices, and we investigated the anti-correlation
and bimodality of these indices. We compared r_CN, the ratio of stars belonging
to the CN-strong and weak groups, with 15 different cluster parameters. We
clearly see bimodal anti-correlation of the CH and CN band stregths in the
metal-rich clusters (Pal12, 47Tuc, NGC6352, NGC5927). Only M15 among the
metal-poor clusters shows a clearly bimodal anti-correlation. We found weak
correlations (sligthly above 1 sigma) of r_CN with the cluster orbital
parameters, present-day total mass, cluster concentration, and age. Our
findings support the self-enrichment scenario, and suggest that the occurrence
of more than two major generations of stars in a GGC should be rare. Small
additional generations (<10-20% of the total) would be difficult to detect with
our samples. The first generation, which corresponds to the CN-weak stars,
usually contains more stars than the second one (=0.82+/-0.29), as
opposed to results based on the Na-O anti-correlations.Comment: 18 pages, 10 figures, 1 electronic table, accepted for publication in
A&A (language edited version