200 research outputs found
AgapeZ1: a Large Amplification Microlensing Event or an Odd Variable Star Towards the Inner Bulge of M31
AgapeZ1 is the brightest and the shortest duration microlensing candidate
event found in the Agape data. It occured only 42" from the center of M31. Our
photometry shows that the half intensity duration of the event6 is 4.8 days and
at maximum brightness we measure a stellar magnitude of R=18.0 with B-R=0.80
mag color. A search on HST archives produced a single resolved star within the
projected event position error box. Its magnitude is R=22.Comment: 4 pages with 5 figure
AGAPE: a microlensing search in the direction of M31
A status report of the microlensing search by the pixel method in the direction of M31, on the 2 meter telescope at Pic du Midi is given. Pixels are stable to a level better than 0.5%. Pixel variations as small as 0.02 magnitude can clearly be detected
The Anomaly in the Candidate Microlensing Event PA-99-N2
The lightcurve of PA-99-N2, one of the recently announced microlensing
candidates towards M31, shows small deviations from the standard Paczynski
form. We explore a number of possible explanations, including correlations with
the seeing, the parallax effect and a binary lens. We find that the
observations are consistent with an unresolved RGB or AGB star in M31 being
microlensed by a binary lens. We find that the best fit binary lens mass ratio
is about one hundredth, which is one of most extreme values found for a binary
lens so far. If both the source and lens lie in the M31 disk, then the standard
M31 model predicts the probable mass range of the system to be 0.02-3.6 solar
masses (95 % confidence limit). In this scenario, the mass of the secondary
component is therefore likely to be below the hydrogen-burning limit. On the
other hand, if a compact halo object in M31 is lensing a disk or spheroid
source, then the total lens mass is likely to lie between 0.09-32 solar masses,
which is consistent with the primary being a stellar remnant and the secondary
a low mass star or brown dwarf. The optical depth (or alternatively the
differential rate) along the line of sight toward the event indicates that a
halo lens is more likely than a stellar lens provided that dark compact objects
comprise no less than 15 per cent (or 5 per cent) of haloes.Comment: Latex, 23 pages, 9 figures, in press at The Astrophysical Journa
Variable stars towards the bulge of M31: the AGAPE catalogue
We present the AGAPE astrometric and photometric catalogue of 1579 variable
stars in a 14'x10' field centred on M31. This work is the first survey devoted
to variable stars in the bulge of M31. The R magnitudes of the objects and the
B-R colours suggest that our sample is dominated by red long-period variable
stars (LPV), with a possible overlap with Cepheid-like type II stars. Twelve
nova candidates are identified. Correlations with other catalogues suggest that
2 novae could be recurrent novae and provide possible optical counterparts for
2 supersoft X-ray sources candidates observed with Chandra.Comment: 11 pages, Latex, accepted for publication in A&
Metabolic and physiological adjustment of Suaeda maritima to combined salinity and hypoxia
BACKGROUND AND AIMS:
Suaeda maritima is a halophyte commonly found on coastal wetlands in the intertidal zone. Due to its habitat S. maritima has evolved tolerance to high salt concentrations and hypoxic conditions in the soil caused by periodic flooding. In the present work, the adaptive mechanisms of S. maritima to salinity combined with hypoxia were investigated on a physiological and metabolic level.
METHODS:
To compare the adaptive mechanisms to deficient, optimal and stressful salt concentrations, S. maritima plants were grown in a hydroponic culture under low, medium and high salt concentrations. Additionally, hypoxic conditions were applied to investigate the impact of hypoxia combined with different salt concentrations. A non-targeted metabolic approach was used to clarify the biochemical pathways underlying the metabolic and physiological adaptation mechanisms of S. maritima .
KEY RESULTS:
Roots exposed to hypoxic conditions showed an increased level of tricarboxylic acid (TCA)-cycle intermediates such as succinate, malate and citrate. During hypoxia, the concentration of free amino acids increased in shoots and roots. Osmoprotectants such as proline and glycine betaine increased in concentrations as the external salinity was increased under hypoxic conditions.
CONCLUSIONS:
The combination of high salinity and hypoxia caused an ionic imbalance and an increase of metabolites associated with osmotic stress and photorespiration, indicating a severe physiological and metabolic response under these conditions. Disturbed proline degradation in the roots induced an enhanced proline accumulation under hypoxia. The enhanced alanine fermentation combined with a partial flux of the TCA cycle might contribute to the tolerance of S. maritima to hypoxic conditions
A Candidate M31/M32 Intergalactic Microlensing Event
We report the discovery of a microlensing candidate projected 2'54" from the
center of M32, on the side closest to M31. The blue color (R-I= 0.00 +/- 0.14)
of the source argues strongly that it lies in the disk of M31, while the
proximity of the line of sight to M32 implies that this galaxy is the most
likely host of the lens. If this interpretation is correct, it would confirm
previous arguments that M32 lies in front of M31. We estimate that of order one
such event or less should be present in the POINT-AGAPE data base. If more
events are discovered in this direction in a dedicated experiment, they could
be used to measure the mass function of M32 up to an unknown scale factor. By
combining microlensing observations of a binary-lens event with a measurement
of the M31-M32 relative proper motion using the astrometric satellites SIM or
GAIA, it will be possible to measure the physical separation of M31 and M32,
the last of the six phase-space coordinates needed to assign M32 an orbit.Comment: Submitted to ApJ Letters. 13 pages, 2 figure
A Short Timescale Candidate Microlensing Event in the POINT-AGAPE Pixel Lensing Survey of M31
We report the discovery of a short-duration microlensing candidate in the
northern field of the POINT-AGAPE pixel lensing survey towards M31. The
full-width half-maximum timescale is very short, just 1.8 days. Almost
certainly, the source star has been identified on Hubble Space Telescope
archival images, allowing us to infer an Einstein crossing time of 10.4 days, a
maximum magnification of about 18, and a lens-source proper motion greater than
0.3 microarcsec/day. The event lies projected at 8' from the center of M31,
which is beyond the bulk of the stellar lens population. The lens is likely to
reside in one of three locations. It may be a star in the M31 disk, or a
massive compact halo object (Macho) in either M31 or the Milky Way. The most
probable mass is 0.06 solar masses for an M31 Macho, 0.02 solar masses for a
Milky Way Macho and 0.2 solar masses for an M31 stellar lens. Whilst the
stellar interpretation is plausible, the Macho interpretation is the most
probable for halo fractions above 20%.Comment: 20 pages, 4 figures, submitted to The Astrophysical Journal (Letters
The Origin of the Universe as Revealed Through the Polarization of the Cosmic Microwave Background
Modern cosmology has sharpened questions posed for millennia about the origin
of our cosmic habitat. The age-old questions have been transformed into two
pressing issues primed for attack in the coming decade: How did the Universe
begin? and What physical laws govern the Universe at the highest energies? The
clearest window onto these questions is the pattern of polarization in the
Cosmic Microwave Background (CMB), which is uniquely sensitive to primordial
gravity waves. A detection of the special pattern produced by gravity waves
would be not only an unprecedented discovery, but also a direct probe of
physics at the earliest observable instants of our Universe. Experiments which
map CMB polarization over the coming decade will lead us on our first steps
towards answering these age-old questions.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 212 author available at http://cmbpol.uchicago.ed
AGAPEROS: Searches for microlensing in the LMC with the Pixel Method; 2, Selection of possible microlensing events
We apply the pixel method of analysis (sometimes called ``pixel lensing'') to a small subset of the EROS-1 microlensing observations of the bar of the Large Magellanic Cloud (LMC). The pixel method is designed to find microlensing events of unresolved source stars and had heretofore been applied only to M31 where essentially all sources are unresolved. With our analysis optimised for the detection of long-duration microlensing events due to 0.01-1 Mo Machos, we detect no microlensing events and compute the corresponding detection efficiencies. We show that the pixel method should detect 10 to 20 times more microlensing events for M>0.05 Mo Machos compared to a classical analysis of the same data which latter monitors only resolved stars. In particular, we show that for a full halo of Machos in the mass range 0.1 -- 0.5 Mo, a pixel analysis of the three-year EROS-1 data set covering 0.39 deg^2 would yield 4 events.We apply the pixel method of analysis (sometimes called ''pixel lensing'') to a small subset of the EROS-1 microlensing observations of the bar of the Large Magellanic Cloud (LMC). The pixel method is designed to find microlensing events of unresolved source stars and had heretofore been applied only to M31 where essentially all sources are unresolved. With our analysis optimised for the detection of long-duration microlensing events due to 0.01-1 Mo Machos, we detect no microlensing events and compute the corresponding detection efficiencies. We show that the pixel method, applied to crowded fields, should detect 10 to 20 times more microlensing events for M>0.05 Mo Machos compared to a classical analysis of the same data which latter monitors only resolved stars. In particular, we show that for a full halo of Machos in the mass range 0.1-0.5 M , a pixel analysis of the three-year EROS-1 data set covering would yield events
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