Searcharxiv⌕ Search

arXiv subjects

J. Kaplan

Publications and source records attributed to J. Kaplan.

At least 55 records · Page 3Linked to original sources
arXiv2004

The POINT-AGAPE Survey I: The Variable Stars in M31

The POINT-AGAPE collaboration has been monitoring M31 for three seasons with the Wide Field Camera on the Isaac Newton Telescope. In each season, data are taken for one hour per night for roughly sixty nights during the six months that M31 is visible. The two fields of view straddle the central bulge, northwards and southwards. We have calculated the locations, periods and amplitudes of 35414 variable stars in M31 as a by-product of our microlensing search. The variables are classified according to their period and amplitude of variation. They are classified into population I and II Cepheids, Miras and semi-regular long-period variables. The population I Cepheids are associated with the spiral arms, while the central concentration of the Miras and long-period variables varies noticeably, the stars with brighter (and shorter) variations being much more centrally concentrated. A crucial role in the microlensing experiment is played by the asymmetry signal. It was initially assumed that the variable stars would not be a serious problem as their distributions would be symmetric. We demonstrate that this assumption is not correct. We find that differential extinction associated with the dust lanes causes the variable star distributions to be asymmetric. The size and direction of the asymmetry of the variable stars is measured as a function of period and amplitude of variation. The implications of this discovery for the successful completion of the microlensing experiments towards M31 are discussed. (Abridged)

astro-ph↗
arXiv2003

Photometric study of two novae in M31

We report $R_cI_c$ light curves of 2 novae in the M31 galaxy which were detected in the four year Nainital Microlensing Survey. One of these novae has been tracked from the initial increase in flux while other has been observed during its descending phase of brightness. The photometry of the first nova during the outburst phase suggests its peak $R_c$ magnitude to be about 17.2 mag with a flux decline rate of 0.11 mag day$^{-1}$ which indicates that it was a fast nova. A month after its outburst, it shows reddening followed by a plateau in $I_c$ flux. The second nova exhibits a bump in $R_c$ and $I_c$, possibly about three weeks after the outburst.

astro-ph↗
arXiv2003

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.

astro-ph↗
arXiv2003

Theory of pixel lensing towards M31 -- II. The velocity anisotropy and flattening of the MACHO distribution

The POINT-AGAPE collaboration is currently searching for massive compact halo objects (MACHOs) towards the Andromeda galaxy (M31). The survey aims to exploit the high inclination of the M31 disk, which causes an asymmetry in the spatial distribution of M31 MACHOs. Here, we investigate the effects of halo velocity anisotropy and flattening on the asymmetry signal using simple halo models. For a spherically symmetric and isotropic halo, we find that the underlying pixel-lensing rate in far-disk M31 MACHOs is more than 5 times the rate of near-disk events. We find that the asymmetry is increased further by about 30% if the MACHOs occupy radial orbits rather than tangential orbits, but is substantially reduced if the MACHOs lie in a flattened halo. However, even for haloes with a minor-to-major axis ratio q = 0.3, the numbers of M31 MACHOs in the far-side outnumber those in the near-side by a factor of ~2. We show that, if positional information is exploited in addition to number counts, then the number of candidate events required to confirm asymmetry for a range of flattened and anisotropic halo models is achievable, even with significant contamination by variable stars and foreground microlensing events. For pixel-lensing surveys which probe a representative portion of the M31 disk, a sample of around 50 candidates is likely to be sufficient to detect asymmetry within spherical haloes, even if half the sample is contaminated, or to detect asymmetry in haloes as flat as q = 0.3 provided less than a third of the sample comprises contaminants. We also argue that, provided its mass-to-light ratio is less than 100, the recently observed stellar stream around M31 is not problematic for the detection of asymmetry. (Abstract slightly abridged.)

astro-ph↗
arXiv2003

First Detection of Polarization of the Submillimetre Diffuse Galactic Dust Emission by Archeops

We present the first determination of the Galactic polarized emission at 353 GHz by Archeops. The data were taken during the Arctic night of February 7, 2002 after the balloon--borne instrument was launched by CNES from the Swedish Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz bolometers mounted in three polarization sensitive pairs that were used for Galactic foreground studies. We present maps of the I, Q, U Stokes parameters over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 microns). They show a significant Galactic large scale polarized emission coherent on the longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization at the level of 4-5%, in agreement with expectations from starlight polarization measurements. Some regions in the Galactic plane (Gem OB1, Cassiopeia) show an even stronger degree of polarization in the range 10-20%. Those findings provide strong evidence for a powerful grain alignment mechanism throughout the interstellar medium and a coherent magnetic field coplanar to the Galactic plane. This magnetic field pervades even some dense clouds. Extrapolated to high Galactic latitude, these results indicate that interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB polarization measurement.

astro-ph↗
arXiv2003

Microlensing towards M31 with MDM data

We report the final analysis of a search for microlensing events in the direction of the Andromeda galaxy, which aimed to probe the MACHO composition of the M31 halo using data collected during the 1998-99 observational campaign at the MDM observatory. In a previous paper, we discussed the results from a first set of observations. Here, we deal with the complete data set, and we take advantage of some INT observations in the 1999-2000 seasons. This merging of data sets taken by different instruments turns out to be very useful, the study of the longer baseline available allowing us to test the uniqueness characteristic of microlensing events. As a result, all the candidate microlensing events previously reported turn out to be variable stars. We further discuss a selection based on different criteria, aimed at the detection of short--duration events. We find three candidates whose positions are consistent with self--lensing events, although the available data do not allow us to conclude unambiguously that they are due to microlensing.

astro-ph↗
arXiv2003

The Point-Agape survey: 4 high signal-to-noise ratio microlensing candidates detected towards M31

We have carried out a survey of the Andromeda galaxy for unresolved microlensing (pixel lensing). We present a subset of four short timescale, high signal-to-noise microlensing candidates found by imposing severe selection criteria: the source flux variation exceeds the flux of an R=21 magnitude star and the full width at half maximum timescale is less than 25 days. Remarkably, in three out of four cases, we have been able to measure or strongly constrain the Einstein crossing time of the event. One event, which lies projected on the M31 bulge, is almost certainly due to a stellar lens in the bulge of M31. The other three candidates can be explained either by stars in M31 and M32 or by MACHOs.

astro-ph↗
arXiv2003

Cosmological constraints from Archeops

We analyze the cosmological constraints that Archeops places on adiabatic cold dark matter models with passive power-law initial fluctuations. Because its angular power spectrum has small bins in l and large l coverage down to COBE scales, Archeops provides a precise determination of the first acoustic peak in terms of position at multipole l_peak=220 +- 6, height and width. An analysis of Archeops data in combination with other CMB datasets constrains the baryon content of the Universe, Omega(b)h^2 = 0.022 (+0.003,-0.004), compatible with Big-Bang nucleosynthesis and with a similar accuracy. Using cosmological priors obtainedfrom recent non-CMB data leads to yet tighter constraints on the total density, e.g. Omega(tot)=1.00 (+0.03,-0.02) using the HST determination of the Hubble constant. An excellent absolute calibration consistency is found between Archeops and other CMB experiments, as well as with the previously quoted best fit model.The spectral index n is measured to be 1.04 (+0.10,-0.12) when the optical depth to reionization, tau, is allowed to vary as a free parameter, and 0.96 (+0.03,-0.04) when tau is fixed to zero, both in good agreement with inflation.

astro-ph↗
arXiv2003

The Cosmic Microwave Background Anisotropy Power Spectrum measured by Archeops

We present a determination by the Archeops experiment of the angular power spectrum of the cosmic microwave background anisotropy in 16 bins over the multipole range l=15-350. Archeops was conceived as a precursor of the Planck HFI instrument by using the same optical design and the same technology for the detectors and their cooling. Archeops is a balloon-borne instrument consisting of a 1.5 m aperture diameter telescope and an array of 21 photometers maintained at ~100 mK that are operating in 4 frequency bands centered at 143, 217, 353 and 545 GHz. The data were taken during the Arctic night of February 7, 2002 after the instrument was launched by CNES from Esrange base (Sweden). The entire data cover ~ 30% of the sky.This first analysis was obtained with a small subset of the dataset using the most sensitive photometer in each CMB band (143 and 217 GHz) and 12.6% of the sky at galactic latitudes above 30 degrees where the foreground contamination is measured to be negligible. The large sky coverage and medium resolution (better than 15 arcminutes) provide for the first time a high signal-to-noise ratio determination of the power spectrum over angular scales that include both the first acoustic peak and scales probed by COBE/DMR. With a binning of Delta(l)=7 to 25 the error bars are dominated by sample variance for l below 200. A companion paper details the cosmological implications.

astro-ph↗
arXiv2002

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.

astro-ph↗
arXiv2001

Microlensing search towards M31

We present the first results of the analysis of data collected during the 1998-99 observational campaign at the 1.3 meter McGraw-Hill Telescope, towards the Andromeda galaxy (M31), aimed to the detection of gravitational microlensing effects as a probe of the presence of dark matter in our and in M31 halo. The analysis is performed using the pixel lensing technique, which consists in the study of flux variations of unresolved sources and has been proposed and implemented by the AGAPE collaboration. We carry out a shape analysis by demanding that the detected flux variations be achromatic and compatible with a Paczynski light curve. We apply the Durbin-Watson hypothesis test to the residuals. Furthermore, we consider the background of variables sources. Finally five candidate microlensing events emerge from our selection. Comparing with the predictions of a Monte Carlo simulation, assuming a standard spherical model for the M31 and Galactic haloes, and typical values for the MACHO mass, we find that our events are only marginally consistent with the distribution of observable parameters predicted by the simulation.

astro-ph↗
arXiv2001

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%.

astro-ph↗
arXiv1999

Destriping of Polarized Data in a CMB Mission with a Circular Scanning Strategy

A major problem in Cosmic Microwave Background (CMB) anisotropy mapping, especially in a total-power mode, is the presence of low-frequency noise in the data streams. If unproperly processed, such low-frequency noise leads to striping in the maps. To deal with this problem, solutions have already been found for mapping the CMB temperature fluctuations but no solution has yet been proposed for the measurement of CMB polarization. Complications arise due to the scan-dependent orientation of the measured polarization. In this paper, we investigate a method for building temperature and polarization maps with minimal striping effects in the case of a circular scanning strategy mission such as the Planck mission.

astro-ph↗
arXiv1998

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.

astro-ph↗
arXiv1998

Destriping Polarised data

We show how to take advantage of a circle scanning strategy, such as that planned for the Planck mission, to get rid of low frequency noises for polarised data.

astro-ph↗
arXiv1996

AGAPE: a search for dark matter towards M31 by microlensing effects on unresolved stars

M31 is a very tempting target for a microlensing search of compact objects in galactic haloes. It is the nearest large galaxy, it probably has its own dark halo, and its tilted position with respect to the line of sight provides an unmistakable signature of microlensing. However most stars of M31 are not resolved and one has to use the ``pixel method'': monitor the pixels of the image rather than the stars. AGAPE is the implementation of this idea. Data have been collected and treated during two autumns of observation at the 2 metre telescope of Pic du Midi. The process of geometric and photometric alignment, which must be performed before constructing pixel light curves, is described. Seeing variations are minimised by working with large super-pixels (2.1) compared with the average seeing. A high level of stability of pixel fluxes, crucial to the approach, is reached. Fluctuations of super-pixels do not exceed 1.7 times the photon noise which is 0.1% of the intensity for the brightest ones. With such stable data, 10 microlensing events are expected for a full ``standard halo''. With a larger field, a regular and short time sampling and a long lever arm in time, the pixel method will be a very efficient tool to explore the halo of M31.

astro-ph↗