2,251 research outputs found
Identification of the Lithium Depletion Boundary and Age of the Southern Open Cluster Blanco 1
We present results from a spectroscopic study of the very low mass members of
the Southern open cluster Blanco 1 using the Gemini-N telescope. We obtained
intermediate resolution (R~4400) GMOS spectra for 15 cluster candidate members
with I~14-20 mag, and employed a series of membership criteria - proximity to
the cluster's sequence in an I/I-Ks color-magnitude diagram (CMD), kinematics
agreeing with the cluster systemic motion, magnetic activity as a youth
indicator - to classify 10 of these objects as probable cluster members. For
these objects, we searched for the presence of the Li I 6708 A feature to
identify the lithium depletion boundary (LDB) in Blanco 1. The I/I-Ks CMD shows
a clear mass segregation in the Li distribution along the cluster sequence;
namely, all higher mass stars are found to be Li-poor, while lower mass stars
are found to be Li-rich. The division between Li-poor and Li-rich (i.e., the
LDB) in Blanco 1 is found at I= and I-Ks=. Using
current pre-main-sequence evolutionary models we determine an LDB age of Myr. Comparing our derived LDB age to upper-main-sequence isochrone
ages for Blanco 1, as well as for other open clusters with identified LDBs, we
find good chronometric consistency when using stellar evolution models that
incorporate a moderate degree of convective core overshoot.Comment: 6 pages, 3 figures, Accepted for Publication in the Astrophysical
Journal Letter
A near-infrared survey for new low-mass members in Alpha Per
We present a near-infrared (K'-band) survey of 0.7 square degree area in the
Alpha Persei open cluster (age = 90 Myr, distance = 182 pc) carried out with
the Omega-Prime camera on the Calar Alto 3.5-m telescope. Combining optical
data (Rc and Ic) obtained with the KPNO/MOSA detector and presented in Stauffer
et al. (1999) with the K' observations, a sample of new candidate members has
been extracted from the optical-infrared colour-magnitude diagram. The location
of these candidates in the colour-colour diagram suggests that two-thirds of
them are actually reddened background giants. About 20 new candidate members
with masses between 0.3 and 0.04 Msun are added to the 400 known Alpha Per
cluster members. If they are indeed Alpha Per members, four of the new
candidates would be brown dwarfs. We discuss the advantages and drawbacks of
the near-infrared survey as compared to the optical selection method. We also
describe the outcome of optical spectroscopy obtained with the Twin
spectrograph on the Calar Alto 3.5-m telescope for about 30 candidates,
including selected members from the optical sample presented in Barrado y
Navascues et al. (2002) and from our joint optical/infrared catalogue. These
results argue in favour of the optical selection method for this particular
cluster.Comment: 13 pages, 10 figures, 3 tables and 1 electronic table, accepted for
publication in A&
Employing a New BVIc Photometric Survey of IC 4665 to Investigate the Age of this Young Open Cluster
We present a new, BVIc photometric survey of the young open cluster IC4665,
which improves on previous studies of this young cluster by incorporating a
rigorous standardization procedure, thus providing high-fidelity colors and
magnitudes for cluster members. We use this new photometric dataset to
reevaluate the properties (age and distance) of IC4665. Namely, using a
statistical approach incorporating Tau^2 CMD modeling, we measure a
pre-main-sequence isochrone age and distance of 36+-9 Myr and 360+-12 pc, as
well as a upper-main-sequence turn-off age and distance of 42+-12 Myr and
357+-12 pc. These ages and distances are highly dependent on the isochrone
model and color used for the fitting procedure, with a possible range of ~10-20
Myr in age and ~20 pc in distance. This spread in calculated ages and distances
seen between colors and models is likely due to limitations in the individual
membership catalogs and/or systematic differences in the predicted stellar
parameters from the different sets of models. Interestingly, when we compare
the isochrone ages for IC4665 to the published lithium depletion boundary age,
28+-5 Myr, we observe that this cluster does not appear to follow the trend of
isochrone ages being 1.5 times smaller than lithium depletion boundary ages. In
addition, comparing the overall magnetic activity (X-ray and H-alpha emission)
in IC4665 with other well studied open clusters, we find the observed activity
distributions for this young cluster are best characterized by assuming an age
of 30-40 Myr, thus in agreement with our pre-main-sequence and turn-off
isochrone ages for IC4665. Overall, although some age discrepancies do exist,
particularly in the ages measured from pre-main-sequence isochrones, the range
of possible IC4665 ages derived from the various dating techniques employed
here is relatively small compared to that found for other well studied open
clusters.Comment: 17 pages, 13 figures, 6 tables; Accepted for publication in the
Astronomical Journa
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