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Search Results: 1 - 10 of 461826 matches for " A. Milsztajn "
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The Galactic Halo from Microlensing
A. Milsztajn
Physics , 2001,
Abstract: The status of the microlensing search for galactic dark matter in the form of massive astronomical compact halo objects (machos) is reviewed. Unresolved issues are discussed, as well as possible ways to solve these.
Not enough stellar mass Machos in the Galactic halo
A. Milsztajn,T. Lasserre,for the EROS collaboration
Physics , 2000, DOI: 10.1016/S0920-5632(00)00970-1
Abstract: We present an update of results from the search for microlensing towards the Large Magellanic Cloud (LMC) by EROS (Experience de Recherche d'Objets Sombres). We have now monitored 25 million stars over three years. Because of the small number of observed microlensing candidates (four), our results are best presented as upper limits on the amount of dark compact objects in the halo of our Galaxy. We discuss critically the candidates and the possible location of the lenses, halo or LMC . We compare our results to those of the MACHO group. Finally, we combine these new results with those from our search towards the Small Magellanic Cloud as well as earlier ones from the EROS1 phase of our survey. The combined data is sensitive to compact objects in the broad mass range $ 10^{-7} - 10 $ solar masses. The derived upper limit on the abundance of stellar mass MACHOs rules out such objects as the dominant component of the Galactic halo if their mass is smaller than 2 solar masses.
Spectroscopic Studies of the Two Eros Candidate Microlensed Stars
J. P. Beaulieu,R. Ferlet,Ph. Grison,A. Vidal-Madjar,J. P. Kneib,E. Maurice,L. Prevot,C. Gry,J. Guibert,O. Moreau,F. Tajahmady,E. Aubourg,P. Bareyre,S. Brehin,M. Gros,M. Lachieze-Rey,B. Laurent,E. Lesquoy,C. Magneville,A. Milsztajn,L. Moscoso,F. Queinnec,J. Rich,M. Spiro,L. Vigroux,S. Zylberajch,R. Ansari,F. Cavalier,M. Moniez
Physics , 1994,
Abstract: Low resolution spectroscopy, and UBVRI photometry, have been obtained for the two EROS microlensing candidates. Radial velocities indicate that both stars are members of the Large Magellanic Cloud. The spectrum and the colours of EROS1, the first candidate, reveal that it is a moderately reddened main-sequence B star with H emission lines. The presence of H absorption lines seems to be more the signature of a normal star than that of a cataclysmic variable. As to EROS2, the second candidate, its spectrum and photometry are those of an unreddened normal main-sequence A star, but it cannot be totally excluded that they represent those of a nova in the pre-outburst phase. Although it is not yet possible to exclude intrinsic stellar variations, the interpretation in terms of microlensing effects remain the most natural one.
SEARCH FOR VERY LOW MASS OBJECTS IN THE GALACTIC HALO
EROS collaboration,E. Aubourg,P. Bareyre,S. Brehin,M. Gros,M. Lachieze-Rey,B. Laurent,E. Lesquoy,C. Magneville,A. Milsztajn,L. Moscoso,F. Queinnec,J. Rich,M. Spiro,L. Vigroux,S. Zylberajch,R. Ansari,F. Cavalier,M. Moniez,J. P. Beaulieu,R. Ferlet,Ph. Grison,A. Vidal-Madjar,E. Maurice,L. Prevot,C. Gry,J. Guibert,O. Moreau,F. Tajahmady
Physics , 1995,
Abstract: We present results from a search for gravitational microlensing of stars in the Large Magellanic Cloud by low mass objects in the Galactic Halo. The search uses the CCD light curves of about 82,000 stars with up to 46 measurements per night over a period of 10 months. No light curve exhibits a form that is consistent with a microlensing event of maximum amplification greater than 1.2. This null result makes it unlikely that the Halo is dominated by objects in the mass range $5 10^{-8}M_{\odot} < M <5 10^{-4}M_{\odot} $. keywords{Galaxy : Halo, kinematics and dynamics, stellar content -- Cosmology : dark matter, gravitational lensing}
New Magellanic Cloud R Coronae Borealis and DY Per type stars from the EROS-2 database: the connection between RCBs, DYPers and ordinary carbon stars
P. Tisserand,P. R. Wood,J. B. Marquette,C. Afonso,J. N. Albert,J. Andersen,R. Ansari,E. Aubourg,P. Bareyre,J. P. Beaulieu,X. Charlot,C. Coutures,R. Ferlet,P. Fouqué,J. F. Glicenstein,B. Goldman,A. Gould,M. Gros,J. de Kat,E. Lesquoy,C. Loup,C. Magneville,E. Maurice,A. Maury,A. Milsztajn,M. Moniez,N. Palanque-Delabrouille,O. Perdereau,J. Rich,P. Schwemling,M. Spiro,A. Vidal-Madjar
Physics , 2009, DOI: 10.1051/0004-6361/200911808
Abstract: R Coronae Borealis stars (RCB) are a rare type of evolved carbon-rich supergiant stars that are increasingly thought to result from the merger of two white dwarfs, called the Double degenerate scenario. This scenario is also studied as a source, at higher mass, of type Ia Supernovae (SnIa) explosions. Therefore a better understanding of RCBs composition would help to constrain simulations of such events. We searched for and studied RCB stars in the EROS Magellanic Clouds database. We also extended our research to DY Per type stars (DYPers) that are expected to be cooler RCBs (T~3500 K) and much more numerous than their hotter counterparts. The light curves of ~70 millions stars have been analysed to search for the main signature of RCBs and DYPers: a large drop in luminosity. Follow-up optical spectroscopy was used to confirm each photometric candidate found. We have discovered and confirmed 6 new Magellanic Cloud RCB stars and 7 new DYPers, but also listed new candidates: 3 RCBs and 14 DYPers. We estimated a range of Magellanic RCB shell temperatures between 360 and 600 K. We confirm the wide range of absolute luminosity known for RCB stars, M_V~-5.2 to -2.6. Our study further shows that mid-infrared surveys are ideal to search for RCB stars, since they have thinner and cooler circumstellar shells than classical post-AGB stars. In addition, by increasing the number of known DYPers by ~400%, we have been able to shed light on the similarities in the spectral energy distribution between DYPers and ordinary carbon stars. We also observed that DYPer circumstellar shells are fainter and hotter than those of RCBs. This suggests that DYPers may simply be ordinary carbon stars with ejection events, but more abundance analysis is necessary to give a status on a possible evolutionnary connexion between RCBs and DYPers.
Metallicity Effects on the Cepheid Extragalactic Distance Scale from EROS photometry in LMC and SMC
D. D. Sasselov,J. P. Beaulieu,C. Renault,P. Grison,R. Ferlet,A. Vidal-Madjar,E. Maurice,L. Prévot,E. Aubourg,P. Bareyre,S. Brehin,C. Coutures,N. Delabrouille,J. de Kat,M. Gros,B. Laurent,M. Lachièze-Rey,E. Lesquoy,C. Magneville,A. Milsztajn,L. Moscoso,F. Queinnec,J. Rich,M. Spiro,L. Vigroux,S. Zylberajch,R. Ansari,F. Cavalier,M. Moniez,C. Gry,J. Guibert,O. Moreau,F. Tajhmady
Physics , 1996,
Abstract: This is an investigation of the period-luminosity relation of classical Cepheids in samples of different metallicity. It is based on 481 Cepheids in the Large and Small Magellanic Clouds from the blue and red filter CCD observations (most similar to V_J & R_J) of the French EROS microlensing project. The data-set is complete and provides an excellent basis for a differential analysis between LMC and SMC. In comparison to previous studies of effects on the PL-relation, the EROS data-set offers extremely well-sampled light curves and well-filled instability strips. This allows reliable separation of Cepheids pulsating in the fundamental and the first overtone mode and derivation of differential reddening. Our main result concerns the determination of distances to galaxies which are inferred by using the LMC as a base and using two color photometry to establish the amount of reddening. We find a zero-point offset between SMC and LMC which amounts to a difference between inferred and true distance modulus of 0.14 \pm 0.06 mag in the VI_c system. The offset is exactly the same in both sets of PL-relations - of the fundamental and of the first overtone mode Cepheids. No effect is seen on the slopes of the PL-relations, although the fundamental and the first overtone mode Cepheids have different PL slopes. We attribute the color and the zero-point offset to the difference in metallicity between the SMC and LMC Cepheids. A metallicity effect of that small magnitude still has important consequencies for the inferred Cepheid distances and the determination of H_0. When applied to recent estimates based on HST Cepheid observations, our metallicity dependence makes the low-H_0 values (Sandage et al. 1994) higher and the high-H_0 values (Freedman et al. 1994b) lower, thus bringing those
The effect of metallicity on the Cepheid distance scale and its implications for the Hubble constant ($H_0$) determination
J. P. Beaulieu,D. D. Sasselov,C. Renault,P. Grison,R. Ferlet,A. Vidal-Madjar,E. Maurice,L. Prévot,E. Aubourg,P. Bareyre,S. Brehin,C. Coutures,N. Delabrouille,J. de Kat,M. Gros,B. Laurent,M. Lachièze-Rey,E. Lesquoy,C. Magneville,A. Milsztajn,L. Moscoso,F. Queinnec,J. Rich,M. Spiro,L. Vigroux,S. Zylberajch,R. Ansari,F. Cavalier,M. Moniez,C. Gry,J. Guibert,O. Moreau,F. Tajhmady
Physics , 1996,
Abstract: Recent HST determinations of the expansion's rate of the Universe (the Hubble constant, H_0) assumed that the Cepheid Period-Luminosity relation at V and I are independent of metallicity (Freedman, et al., 1996, Saha et al., 1996, Tanvir et al., 1995). The three groups obtain different vales for H_0. We note that most of this discrepancy stems from the asumption (by both groups) that the Period-Luminosity relation is independent of metallicity. We come to this conclusion as a result of our study of the Period-Luminosity relation of 481 Cepheids with 3 millions two colour measurements in the Large Magellanic Cloud and the Small Magellanic Cloud obtained as a by-product of the EROS microlensing survey. We find that the derived interstellar absorption corrections are particularly sensitive to the metallicity and when our result is applied to recent estimates based on HST Cepheids observations it makes the low-H_0 values higher and the high-H_0 value lower, bringing those discrepant estimates into agrement around $H_0 \approx 70 km/s Mpc^{-1}$.
EROS VARIABLE STARS : FUNDAMENTAL-MODE AND FIRST OVERTONE CEPHEIDS IN THE BAR OF THE LARGE MAGELLANIC CLOUD
J. P. Beaulieu,P. Grison,W. Tobin,J. D. Pritchard,R. Ferlet,A. Vidal-Madjar,E. Maurice,L. Prevot,C. Gry,J. Guibert,O. Moreau,F. Tajahmady,E. Aubourg,P. Bareyre,S. Brehin,M. Gros,M. Lachieze-Rey,B. Laurent,E. Lesquoy,C. Magneville,A. Milsztajn,L. Moscoso,F. Queinnec,J. Rich,M. Spiro,L. Vigroux,S. Zylberajch,R. Ansari,F. Cavalier,M. Moniez
Physics , 1995,
Abstract: We present CCD phase-binned light curves at 490 nm for 97 Cepheid variable stars in the bar of the LMC. The photometry was obtained as part of the French EROS project and has excellent phase coverage, permitting accurate decomposition into Fourier components. We identify as `sinusoidal' or s-Cepheids those stars with periods less than 5.5 d and small second-harmonic components. These stars comprise $\sim$30% of our sample and most form a sequence $\sim$1 mag brighter than the LMC classical Cepheids in the period-luminosity diagram. They are also generally bluer and have lower-amplitude light curves. We infer that the s-Cepheids are first-overtone pulsators because, when their periods are converted to expected fundamental-mode values, they obey a common period-luminosity-colour relation with classical Cepheids. This also confirms the reality of the colour term in the Cepheid period-luminosity-colour relation. Further, the blue edge of the classical Cepheid instability strip agrees well with the theoretical calculations for the fundamental mode made by Chiosi et al. (1993) for the Hertzsprung-Russell and period-luminosity diagrams, but we find that our observed s-Cepheids are $>0.2$ mag brighter and bluer than the Chiosi et al.\ predictions for the first-overtone. We identify a number of features in plots of our stars' Fourier-component amplitude ratios and phase differences. These features have been identified with resonances between different pulsation modes. In the LMC we find these features seem to occur at periods very similar to Galactic ones for classical Cepheids, but at different periods for s-Cepheids. We discover a double-mode Cepheid in the LMC, for which $P({\rm first overtone})/P({\rm fundamental}) = 0.710 \pm 0.001$, very similar to observed ratios for Galactic double-mode Cepheids.
EROS Variable Stars : Discovery of Beat Cepheids in the Small Magellanic Cloud and the effect of metallicity on pulsation
J. P. Beaulieu,M. Krockenberger,D. D. Sasselov,C. Renault,R. Ferlet,A. Vidal-Madjar,E. Maurice,L. Prévot,E. Aubourg,P. Bareyre,S. Brehin,C. Coutures,N. Delabrouille,J. de Kat,M. Gros,B. Laurent,M. Lachièze-Rey,E. Lesquoy,C. Magneville,A. Milsztajn,L. Moscoso,F. Queinnec,J. Rich,M. Spiro,L. Vigroux,S. Zylberajch,R. Ansari,F. Cavalier,M. Moniez,C. Gry.
Physics , 1997,
Abstract: We report the discovery of eleven beat Cepheids in the Small Magellanic Cloud, using data obtained by the EROS microlensing survey. Four stars are beating in the fundamental and first overtone mode (F/1OT), seven are beating in the first and second overtone (1OT/2OT). The SMC F/1OT ratio is systematically higher than the LMC F/1OT, while the 1OT/2OT period ratio in the SMC Cepheids is the same as the LMC one.
Type Ia supernova rate at $z \sim 0.1$
D. Hardin,C. Afonso,C. Alard,J. N. Albert,A. Amadon,J. Andersen,R. Ansari,é. Aubourg,P. Bareyre,F. Bauer,J. P. Beaulieu,G. Blanc,A. Bouquet,S. Char,X. Charlot,F. Couchot,C. Coutures,F. Derue,R. Ferlet,J. F. Glicenstein,B. Goldman,A. Gould,D. Graff,M. Gros,J. Haissinski,J. C. Hamilton,J. de Kat,A. Kim,T. Lasserre,é. Lesquoy,C. Loup,C. Magneville,B. Mansoux,J. B. Marquette,é. Maurice,A. Milsztajn,M. Moniez,N. Palanque-Delabrouille,O. Perdereau,L. Prévot,N. Regnault,J. Rich,M. Spiro,A. Vidal-Madjar,L. Vigroux,S. Zylberajch,The EROS collaboration
Physics , 2000,
Abstract: We present the EROS nearby supernova ($z \sim 0.02 - 0.2$) search and the analysis of the first year of data (1997). A total of 80 square degrees were surveyed. Eight supernov{\ae} were detected, four of which were spectroscopically identified as type Ia supernov{\ae}. The search efficiency was determined with a Monte-Carlo simulation taking into account the efficiencies for both supernova detection and host galaxy identification. Assuming that for a given galaxy the supernova rate is proportional to the galactic luminosity, we compute a type Ia supernova explosion rate of: ${\cal R} = 0.44 {}_{-0.21}^{+0.35} {}_{-0.07}^{+0.13} h^2: / 10^{10} \lbsun / 100 {\rm yrs}$ at an average redshift of $\sim 0.1$ where the errors are respectively statistical and systematic (type misidentification included).
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