545 research outputs found
Monte Carlo analysis of the MEGA microlensing events towards M31
We perform an analytical study and a Monte Carlo (MC) analysis of the main
features for microlensing events in pixel lensing observations towards M31. Our
main aim is to investigate the lens nature and location of the 14 candidate
events found by the MEGA collaboration. Assuming a reference model for the mass
distribution in M31 and the standard model for our galaxy, we estimate the
MACHO-to-self lensing probability and the event time duration towards M31.
Reproducing the MEGA observing conditions, as a result we get the MC event
number density distribution as a function of the event full-width half-maximum
duration and the magnitude at maximum . For a
MACHO mass of we find typical values of day
and , for both MACHO-lensing and self-lensing
events occurring beyond about 10 arcminutes from the M31 center. A comparison
of the observed features ( and ) with our MC
results shows that for a MACHO mass the four innermost MEGA
events are most likely self-lensing events, whereas the six outermost events
must be genuine MACHO-lensing events.Comment: in press on A&
Measuring Polarization in microlensing events
We re-consider the polarization of the star light that may arise during
microlensing events due to the high gradient of magnification across the
atmosphere of the source star, by exploring the full range of microlensing and
stellar physical parameters. Since it is already known that only cool evolved
giant stars give rise to the highest polarization signals, we follow the model
by Simmons et al. (2002) to compute the polarization as due to the photon
scattering on dust grains in the stellar wind. Motivated by the possibility to
perform a polarization measurement during an ongoing microlensing event, we
consider the recently reported event catalog by the OGLE collaboration covering
the 2001-2009 campaigns (OGLE-III events), that makes available the largest and
more comprehensive set of single lens microlensing events towards the Galactic
bulge. The study of these events, integrated by a Monte Carlo analysis, allows
us to estimate the expected polarization profiles and to predict for which
source stars and at which time is most convenient to perform a polarization
measurement in an ongoing event. We find that about two dozens of OGLE-III
events (about 1 percent of the total) have maximum polarization degree in the
range 0.1 < P_{\rm max} <1 percent, corresponding to source stars with apparent
magnitude I < 14.5, being very cool red giants.This signal is measurable by
using the FORS2 polarimeter at VLT telescope with about 1 hour integration
time.Comment: Originally submitted to MNRAS on 01/07/2014. Present version with
minor changes as required by the Refere
Pixel lensing as a way to detect extrasolar planets in M31
We study the possibility to detect extrasolar planets in M31 through pixel-lensing observations. Using a Monte Carlo approach, we select the physical parameters of the binary lens system, a star hosting a planet, and we calculate the pixel-lensing light curve taking into account the finite source effects. Indeed, their inclusion is crucial since the sources in M31 microlensing events are mainly giant stars. Light curves with detectable planetary features are selected by looking for significant deviations from the corresponding Paczyński shapes. We find that the time-scale of planetary deviations in light curves increase (up to 3-4 d) as the source size increases. This means that only few exposures per day, depending also on the required accuracy, may be sufficient to reveal in the light curve a planetary companion. Although the mean planet mass for the selected events is about , even small mass planets (MP < 20 M⊕) can cause significant deviations, at least in the observations with large telescopes. However, even in the former case, the probability to find detectable planetary features in pixel-lensing light curves is at most a few per cent of the detectable events, and therefore many events have to be collected in order to detect an extrasolar planet in M31. Our analysis also supports the claim that the anomaly found in the candidate event PA-99-N2 towards M31 can be explained by a companion object orbiting the lens sta
Measuring polarization in microlensing events
We reconsider the polarization of the star light that may arise during microlensing events due to the high gradient of magnification across the atmosphere of the source star, by exploring the full range of microlensing and stellar physical parameters. Since it is already known that only cool evolved giant stars give rise to the highest polarization signals, we follow the model by Simmons etal. to compute the polarization as due to the photon scattering on dust grains in the stellar wind. Motivated by the possibility to perform a polarization measurement during an ongoing microlensing event, we consider the recently reported event catalogue by the Optical Gravitational Lensing Experiment (OGLE) collaboration covering the 2001-2009 campaigns (OGLE-III events), that makes available the largest and more comprehensive set of single-lens microlensing events towards the Galactic bulge. The study of these events, integrated by a Monte Carlo analysis, allows us to estimate the expected polarization profiles and to predict for which source stars and at which time is most convenient to perform a polarization measurement in an ongoing event. We find that about two dozens of OGLE-III events (about 1 per cent of the total) have maximum polarization degree in the range 0.1<Pmax<1 per cent, corresponding to source stars with apparent magnitude I≲14.5, being very cool red giants. This signal is measurable by using the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at Very Large Telescope (VLT) telescope with about 1h integration tim
Treatment of a double-giant Rhinophyma with electrocautery and Versajet hydrosurgery system
Rhinophyma is a disfiguring condition etiologically related to rosacea and due to hypertrophy of the sebaceous glands of the nose. It leads to a progressive thickening of the skin up to the development, in some cases, of severe deformities that result in significant functional deficits and serious cosmetic damage. We report a case of giant rhinophyma consisting of 2 large masses that interfered with feeding and respiration of the patient, and we describe the surgical treatment by resection with electrosurgery and razor-thin saline jet (Versajet Hydrosurgery System). This combined approach is simple and effective for the treatment of severe cases of rhinophyma
M31 Pixel Lensing PLAN Campaign: MACHO Lensing and Self Lensing Signals
We present the final analysis of the observational campaign carried out by
the PLAN (Pixel Lensing Andromeda) collaboration to detect a dark matter signal
in form of MACHOs through the microlensing effect. The campaign consists of
about 1 month/year observations carried out during 4 years (2007-2010) at the
1.5m Cassini telescope in Loiano ("Astronomical Observatory of BOLOGNA", OAB)
plus 10 days of data taken in 2010 at the 2m Himalayan Chandra Telescope (HCT)
monitoring the central part of M31 (two fields of about 13'x12.6'). We
establish a fully automated pipeline for the search and the characterization of
microlensing flux variations: as a result we detect 3 microlensing candidates.
We evaluate the expected signal through a full Monte Carlo simulation of the
experiment completed by an analysis of the detection efficiency of our
pipeline. We consider both "self lensing" and "MACHO lensing" lens populations,
given by M31 stars and dark matter halo MACHOs, in the M31 and the Milky Way
(MW), respectively. The total number of events is compatible with the expected
self-lensing rate. Specifically, we evaluate an expected signal of about 2
self-lensing events. As for MACHO lensing, for full 0.5 (0.01) solar mass MACHO
halos, our prediction is for about 4 (7) events. The comparatively small number
of expected MACHO versus self lensing events, together with the small number
statistics at disposal, do not enable us to put strong constraints on that
population. Rather, the hypothesis, suggested by a previous analysis, on the
MACHO nature of OAB-07-N2, one of the microlensing candidates, translates into
a sizeable lower limit for the halo mass fraction in form of the would be MACHO
population, f, of about 15% for 0.5 solar mass MACHOs.Comment: ApJ accepted, 13 pages, 5 figures, 2 table
Exoplanet Searches in the Habitable Zone with Gravitational Microlensing
There are different methods for finding exoplanets such as radial spectral shifts, astrometrical measurements, transits, timing, etc. Gravitational microlensing (including pixel-lensing) is among the most promising techniques with the potential of detecting Earth-like planets at distances about a few astronomical units from their host stars. Here we emphasize the importance of polarization measurements which can help to resolve degeneracies in theoretical models. In particular, the polarization angle could give additional information about the relative position of the lens with respect to the sourc
Pixel-lensing as a way to detect extrasolar planets in M31
We study the possibility to detect extrasolar planets in M31 through
pixel-lensing observations. Using a Monte Carlo approach, we select the
physical parameters of the binary lens system, a star hosting a planet, and we
calculate the pixel-lensing light curve taking into account the finite source
effects. Indeed, their inclusion is crucial since the sources in M31
microlensing events are mainly giant stars. Light curves with detectable
planetary features are selected by looking for significant deviations from the
corresponding Paczy\'{n}ski shapes. We find that the time scale of planetary
deviations in light curves increase (up to 3-4 days) as the source size
increases. This means that only few exposures per day, depending also on the
required accuracy, may be sufficient to reveal in the light curve a planetary
companion. Although the mean planet mass for the selected events is about , even small mass planets () can
cause significant deviations, at least in the observations with large
telescopes. However, even in the former case, the probability to find
detectable planetary features in pixel-lensing light curves is at most a few
percent of the detectable events, and therefore many events have to be
collected in order to detect an extrasolar planet in M31. Our analysis also
supports the claim that the anomaly found in the candidate event PA-99-N2
towards M31 can be explained by a companion object orbiting the lens star.Comment: Accepted for publication on Monthly Notices of the Royal Astronomical
Society (MNRAS), 200
Slott-Agape Project
SLOTT-AGAPE (Systematic Lensing Observation at Toppo Telescope - Andromeda
Gravitational Amplification Pixel Lensing Experiment) is a new collaboration
project among international partners from England, France, Germany, Italy and
Switzerland that intends to perform microlensing observation by using M31 as
target. The MACHOs search is made thanks to the pixel lensing technique.Comment: 4 pages, 2 figures, proceeding of XLIII Congresso della Societa'
Astronomica Italiana, Napoli, 4-8 Maggio, 199
- …