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The relationship between CK and CV chondrites: a single parent body source?
The relationship between CK and CV3 chondrites is examined. Both groups may represent a single continuum and have been derived from the same parent body
The hydrogen isotopic composition of fossil micrometeorites: Implications for the origin of water on Earth.
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The relationship between CK and CV chondrites
CK chondrites are highly oxidized meteorites containing abundant magnetite and trace amounts of Fe,Ni metal. Although the group is predominately composed of equilibrated meteorites (types 4–6), in recent years a significant number of new samples have been classified as being either CK3 or CK3-anomalous. These unequilibrated CKs often display a close affinity with members of the CV oxidized subgroup. CKs and CVs (oxidized subgroup) may therefore form a continuum and by implication could be derived from a single common parent body. To investigate the relationship between these two groups a detailed study of the oxygen isotope composition, opaque mineralogy and major and trace element geochemistry of a suite of CV and CK chondrites has been undertaken. The results of oxygen isotope analysis confirm the close affinity between CV and CK chondrites, while excluding the possibility of a linkage between the CO and CK groups. Magnetites in both CV and CK chondrites show significant compositional similarities, but high Ti contents are a diagnostic feature of the latter group. The results of major and trace element analysis demonstrate that both CV and CK chondrites show overlapping variation. Supporting evidence for a single common source for both groups comes from their similar cosmic-ray exposure age distributions. Recent reflectance spectral analysis is consistent with both the CVs and CKs being derived from Eos family asteroids, which are believed to have formed by the catastrophic disruption of a single large asteroid. Thus, a range of evidence appears to be consistent with CV and CK chondrites representing samples from a single thermally stratified parent body. In view of the close similarity between CV and CK chondrites some modification of the present classification scheme may be warranted, possibly involving integration of the two groups. One means of achieving this would be to reassigned CK chondrites to a subgroup of the oxidized CVs. It is recognized that a full evaluation of this proposal may require further study of the still poorly understood CK3 chondrites
Microlensing in the double quasar SBS1520+530
We present the results of a monitoring campaign of the double quasar
SBS1520+530 at Maidanak observatory from April 2003 to August 2004. We obtained
light curves in V and R filters that show small-amplitude \Delta m~0.1 mag
intrinsic variations of the quasar on time scales of about 100 days. The data
set is consistent with the previously determined time delay of \Delta
t=(130+-3) days by Burud et al. (2002). We find that the time delay corrected
magnitude difference between the quasar images is now larger by (0.14+-0.03)
mag than during the observations by Burud et al. (2002). This confirms the
presence of gravitational microlensing variations in this system.Comment: 6 pages, 7 figures. Accepted for publication in A&
A boxy bulge in the Milky Way. Inversion of the stellar statistics equation with 2MASS data
Inverting the stellar statistics equation from 2MASS star counts, we obtain
the 3D density distribution of the Galactic bulge as well as its luminosity
function in the K-band. This results in a boxy bulge with axial ratios
1:0.5:0.4 and a major axis angle with respect to the Sun-galactic center of
.Comment: 5 pages, accepted to be published in A&
Optical Observations of SAX J1808.4-3658 During Quiescence
We observed the accreting millisecond pulsar SAX J1808.4-3658 with
Gemini-South in g' and i' bands, nearly simultaneous with XMM-Newton
observations. A clear periodic flux modulation on the system's orbital period
is present, consistent with the varying aspect of the donor star's heated face.
We model the contributions of a disk and donor star to these optical bands. To
produce the observed modulation amplitudes, we conclude that the donor must be
irradiated by an external flux 2 orders of magnitude greater than provided by
the measured X-ray luminosity. A possible explanation for this irradiation is
that the radio pulsar mechanism becomes active during the quiescent state as
suggested by Burderi et al., with relativistic particles heating the donor's
day-side face. Our modelling constrains the binary inclination to be between 36
and 67 degrees. We obtain estimates for the pulsar mass of >2.2 solar masses
(although this limit is sensitive to the source's distance), consistent with
the accelerated NS cooling in this system indicated by X-ray observations. We
also estimate the donor mass to be in the range of 0.07-0.11 solar masses,
providing further indications that the system underwent non-standard binary
evolution to reach its current state.Comment: 11 pages, 10 figures, accepted for publication in MNRA
Modelling the Galactic Bar Using Red Clump Giants
The color-magnitude diagrams of stars obtained for 12
fields across the Galactic bulge with the OGLE project reveal a well-defined
population of bulge red clump giants. We find that the distributions of the
apparent magnitudes of the red clump stars are systematically fainter when
moving towards lower galactic fields. The most plausible explanation of
this distinct trend is that the Galactic bulge is a bar, whose nearest end lies
at positive galactic longitude. We model this Galactic bar by fitting for all
fields the observed luminosity functions in the red clump region of the
color-magnitude diagram. We find that almost regardless of the analytical
function used to describe the 3-D stars distribution of the Galactic bar, the
resulting models have the major axis inclined to the line of sight by
, with axis ratios corresponding to . This
puts a strong constraint on the possible range of the Galactic bar models.
Gravitational microlensing can provide us with additional constrains on the
structure of the Galactic bar.Comment: submitted to the New Astronomy, 27 pages, 11 figures; also available
at ftp://www.astro.princeton.edu/stanek/Barmodel and through WWW at
http://www.astro.princeton.edu/~library/prep.htm
An R- and I-Band Photometric Variability Survey of the Cygnus OB2 Association
We present a catalog of photometrically variable stars discovered within two
21'.3 X 21'.3 fields centered on the Cygnus OB2 association. There have
hitherto been no deep optical variability studies of Cyg OB2 despite it being
replete with early-type massive stars, perhaps due to the high and variable
extinction (up to A_V ~ 20) that permeates much of the region. Here we provide
results of the first variability study with this combination of spatial
coverage (~ 0.5 deg) and photometric depth (R ~ 21 mag). We find 121 stars to
be variable in both R- and I-band, 116 of them newly discovered. Of the 121
variables, we identify 27 eclipsing binaries (EBs) and eclipsing binary
candidates, 20 potential Herbig Ae/Be stars, and 52 pulsating variables.
Confirming both the status and the cluster membership of the Herbig Ae/Be stars
would address the uncertainty regarding the age and star formation history of
Cyg OB2. We match our catalog to known variables and binaries in the region,
2MASS near-IR (NIR) data, and Chandra X-ray observations to find counterparts
to new variables in other wavelengths.Comment: 34 pages, 12 figures, submitted to Ap
A 2.15 Hour Orbital Period for the Low Mass X-Ray Binary XB 1832-330 in the Globular Cluster NGC 6652
We present a candidate orbital period for the low mass X-ray binary XB
1832-330 in the globular cluster NGC 6652 using a 6.5 hour Gemini South
observation of the optical counterpart of the system. Light curves in g' and r'
for two LMXBs in the cluster, sources A and B in previous literature, were
extracted and analyzed for periodicity using the ISIS image subtraction
package. A clear sinusoidal modulation is evident in both of A's curves, of
amplitude ~0.11 magnitudes in g' and ~0.065 magnitudes in r', while B's curves
exhibit rapid flickering, of amplitude ~1 magnitude in g' and ~0.5 magnitudes
in r'. A Lomb-Scargle test revealed a 2.15 hour periodic variation in the
magnitude of A with a false alarm probability less than 10^-11, and no
significant periodicity in the light curve for B. Though it is possible
saturated stars in the vicinity of our sources partially contaminated our
signal, the identification of A's binary period is nonetheless robust.Comment: 7 pages, 7 figures, ApJ in pres
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