arXiv subjects

J. B. Marquette

Publications and source records attributed to J. B. Marquette.

42 records · Page 3Linked to original sources

arXiv2004

EROS 2 photometry of probable R Coronae Borealis stars in the Small Magellanic Cloud

EROS 2 (Experience de Recherche d'Objets Sombres) conducted a survey of the SMC between July 1996 and February 2003 in two EROS broad-band colours, V_E and R_E. The photometric data of 4.2 million stars have been searched for behaviour typical of R Coronae Borealis (RCB) candidates such as drastic changes in magnitude. Five objects have been found, four of them being catalogued in the Simbad database as RAW 21, RAW 233, RAW 476, and [MH95] 431 with confirmed carbon-rich atmospheres, characteristic of RCB. From the EROS 2 light curve of RAW 21 and its spectrum reported by Morgan et al. (2003), we confirm that it is the first RCB to be found in the SMC. The other objects are new RCB candidates with absolute luminosity and colour close to those found for RCBs in the LMC. We propose that 2 of them are DY Per-like RCBs.

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arXiv2004

Type Ia supernova rate at a redshift of ~ 0.1

We present the type Ia rate measurement based on two EROS supernova search campaigns (in 1999 and 2000). Sixteen supernovae identified as type Ia were discovered. The measurement of the detection efficiency, using a Monte Carlo simulation, provides the type Ia supernova explosion rate at a redshift ~ 0.13. The result is $0.125^{+0.044+0.028}_{-0.034-0.028} h_{70}^2$ SNu where 1 SNu = 1 SN / $10^{10} L_{sun}^B$ / century. This value is compatible with the previous EROS measurement (Hardin et al. 2000), done with a much smaller sample, at a similar redshift. Comparison with other values at different redshifts suggests an evolution of the type Ia supernova rate.

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arXiv2004

Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlense H alpha line

We discuss high-resolution, time-resolved spectra of the caustic exit of the binary microlensing event OGLE 2002-BUL-69 obtained with UVES on the VLT. The source star is a G5III giant in the Galactic Bulge. During such events, the source star is highly magnified, and a strong differential magnification around the caustic resolves its surface. Using an appropriate model stellar atmosphere generated by the NextGEN code we obtained a model light curve for the caustic exit and compared it with a dense set of photometric observations obtained by the PLANET microlensing follow up network. We further compared predicted variations in the H alpha equivalent width with those measured from our spectra. While the model and observations agree in the gross features, there are discrepancies suggesting shortcomings in the model, particularly for the H alpha line core, where we have detected amplified emission from the stellar chromosphere as the source star's trailing limb exited the caustic. This achievement became possible by the provision of the OGLE-III Early Warning System, a network of small telescopes capable of nearly-continuous round-the-clock photometric monitoring, on-line data reduction, daily near-real-time modelling in order to predict caustic crossing parameters, and a fast and efficient response of a 8m-class telescope to a ``Target-Of-Opportunity'' observation request.

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arXiv2002

Observation of periodic variable stars towards the galactic spiral arms by EROS II

We present the results of a massive variability search based on a photometric survey of a six square degree region along the Galactic plane at ($l = 305^\circ$, $b = -0.8^\circ$) and ($l = 330^\circ$, $b = -2.5^\circ$). This survey was performed in the framework of the EROS II (Expérience de Recherche d'Objets Sombres) microlensing program. The variable stars were found among 1,913,576 stars that were monitored between April and June 1998 in two passbands, with an average of 60 measurements. A new period-search technique is proposed which makes use of a statistical variable that characterizes the overall regularity of the flux versus phase diagram. This method is well suited when the photometric data are unevenly distributed in time, as is our case. 1,362 objects whose luminosity varies were selected. Among them we identified 9 Cepheids, 19 RR Lyrae, 34 Miras, 176 eclipsing binaries and 266 Semi-Regular stars. Most of them are newly identified objects. The cross-identification with known catalogues has been performed. The mean distance of the RR Lyrae is estimated to be $\sim 4.9 \pm 0.3$ kpc undergoing an average absorption of $\sim 3.4 \pm 0.2$ magnitudes. This distance is in good agreement with the one of disc stars which contribute to the microlensing source star population.Our catalogue and light curves are available electronically from the CDS, Strasbourg and from our Web site http://eros.in2p3.fr.

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arXiv2001

Blue irregular variable stars in the Small Magellanic Cloud from EROS2 : Herbig Ae/Be or classical Be stars ?

Using data from the EROS2 microlensing survey, we report the discovery of two blue objects with irregular photometric behaviour of $ΔV \sim 0.1$-0.4 mag on time scales of 20 to 200 days. They show a bluer when fainter behaviour. Subsequent spectra taken with the ESO 3.6m telescope show spectral type B4eIII and B2eIV-V with strong $H α$ emission. These objects resemble the Herbig AeBe but also classical Be stars. At this stage, it is not possible to distinguish unambiguously between pre-main sequence and classical Be nature. If we favour the pre-main sequence interpretation, they are more luminous than the luminosity upper limit for Galactic HAeBe stars. The same was found for the HAeBe candidates in the LMC. This might be due to a shorter accretion time scale ($τ= M_*/\dot{M}$), or the smaller dust content during the pre-main sequence evolution of SMC and LMC stars.

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arXiv2000

Type Ia supernova rate at $z \sim 0.1$

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 supernovæ were detected, four of which were spectroscopically identified as type Ia supernovæ. 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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