687 research outputs found
WIYN Open Cluster Study. XXXVIII. Stellar Radial Velocities in the Young Open Cluster M35 (NGC 2168)
We present 5201 radial-velocity measurements of 1144 stars, as part of an
ongoing study of the young (150 Myr) open cluster M35 (NGC 2168). We have
observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN
3.5m telescope. Our stellar sample covers main-sequence stars over a magnitude
range of 13.0<V<16.5 (1.6 - 0.8 Msun) and extends spatially to a radius of 30
arcminutes (7 pc in projection at a distance of 805 pc or 4 core radii). Due to
its youth, M35 provides a sample of late-type stars with a range of rotation
periods. Therefore, we analyze the radial-velocity measurement precision as a
function of the projected rotational velocity. For narrow-lined stars (v sin i
< 10 km/s), the radial velocities have a precision of 0.5 km/s, which degrades
to 1.0 km/s for stars with v sin i = 50 km/s. The radial-velocity distribution
shows a well-defined cluster peak with a central velocity of -8.16 +/- 0.05
km/s, permitting a clean separation of the cluster and field stars. For stars
with >=3 measurements, we derive radial-velocity membership probabilities and
identify radial-velocity variables, finding 360 cluster members, 55 of which
show significant radial- velocity variability. Using these cluster members, we
construct a color-magnitude diagram for our stellar sample cleaned of field
star contamination. We also compare the spatial distribution of the single and
binary cluster members, finding no evidence for mass segregation in our stellar
sample. Accounting for measurement precision, we place an upper limit on the
radial-velocity dispersion of the cluster of 0.81 +/- 0.08 km/s. After
correcting for undetected binaries, we derive a true radial-velocity dispersion
of 0.65 +/- 0.10 km/s.Comment: accepted for publication in A
Spectroscopic membership for the populous 300 Myr-old open cluster NGC 3532
NGC 3532 is an extremely rich open cluster embedded in the Galactic disc,
hitherto lacking a comprehensive, documented membership list. We provide
membership probabilities from new radial velocity observations of solar-type
and low-mass stars in NGC 3532, in part as a prelude to a subsequent study of
stellar rotation in the cluster. Using extant optical and infra-red photometry
we constructed a preliminary photometric membership catalogue, consisting of
2230 dwarf and turn-off stars. We selected 1060 of these for observation with
the AAOmega spectrograph at the Anglo-Australian Telescope and 391 stars for
observations with the Hydra-South spectrograph at the Victor Blanco Telescope,
obtaining spectroscopic observations over a decade for 145 stars. We measured
radial velocities for our targets through cross-correlation with model spectra
and standard stars, and supplemented them with radial velocities for 433
additional stars from the literature. We also measured log g, Teff, and [Fe/H]
from the AAOmega spectra. Together with proper motions from Gaia DR2 we find
660 exclusive members. The members are distributed across the whole cluster
sequence, from giant stars to M dwarfs, making NGC 3532 one of the richest
Galactic open clusters known to date, on par with the Pleiades. From further
spectroscopic analysis of 153 dwarf members we find the metallicity to be
marginally sub-solar, with [Fe/H]=-0.07. Exploiting trigonometric parallax
measurements from Gaia DR2 we find a distance of pc. Based on
the membership we provide an empirical cluster sequence in multiple photometric
passbands. A comparison of the photometry of the measured cluster members with
several recent model isochrones enables us to confirm the 300 Myr cluster age.
However, all of the models evince departures from the cluster sequence in
particular regions, especially in the lower mass range. (abridged)Comment: Accepted for publication in A&A. 19 pages, 18 Figures, and 6 Table
The possible existence of Hs in nature from a geochemical point of view
A hypothesis of the existence of a long-lived isotope 271Hs in natural
molybdenites and osmirides is considered from a geochemical point of view. It
is shown that the presence of Hs in these minerals can be explained only by
making an additional ad hoc assumption on the existence of an isobaric pair of
271Bh-271Hs. This assumption could be tested by mass-spectrometric measurements
of U, Pb, Kr, Xe, and Zr isotopic shifts.Comment: 5 pages, no figures. Physics of Particles and Nuclei Letters, 2006,
Vol. 3, No. 3, pp. 165-168 in pres
Photometric Variability in Kepler Target Stars: The Sun Among Stars -- A First Look
The Kepler mission provides an exciting opportunity to study the lightcurves
of stars with unprecedented precision and continuity of coverage. This is the
first look at a large sample of stars with photometric data of a quality that
has heretofore been only available for our Sun. It provides the first
opportunity to compare the irradiance variations of our Sun to a large cohort
of stars ranging from vary similar to rather different stellar properties, at a
wide variety of ages. Although Kepler data is in an early phase of maturity,
and we only analyze the first month of coverage, it is sufficient to garner the
first meaningful measurements of our Sun's variability in the context of a
large cohort of main sequence stars in the solar neighborhood. We find that
nearly half of the full sample is more active than the active Sun, although
most of them are not more than twice as active. The active fraction is closer
to a third for the stars most similar to the Sun, and rises to well more than
half for stars cooler than mid K spectral types.Comment: 13 pages, 4 figures, accepted to ApJ Letter
Deep MMT Transit Survey of the Open Cluster M37 I: Observations and Cluster Parameters
We have conducted a deep (15 \la r \la 23), 20 night survey for transiting
planets in the intermediate age open cluster M37 (NGC 2099) using the Megacam
wide-field mosaic CCD camera on the 6.5m Multiple Mirror Telescope (MMT). In
this paper we describe the observations and data reduction procedures for the
survey and analyze the stellar content and dynamical state of the cluster. By
combining high resolution spectroscopy with existing and new
color magnitude diagrams we determine the fundamental cluster parameters:
Myr without overshooting ( with
overshooting), , and
which are in good agreement with, though more
precise than, previous measurements. We determine the mass function down to
and use this to estimate the total cluster mass of .Comment: 65 pages, 21 figures, 11 tables. Accepted for publication in Ap
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