arXiv subjects

Gaspard Duchene

Publications and source records attributed to Gaspard Duchene.

57 records · Page 4Linked to original sources

arXiv1999

Accretion in Taurus PMS binaries: a spectroscopic study

We present low-resolution optical spectra of each component of 10 T Tauri (TT) binary systems with separations ranging from 0.9" to 3.5" and located in the Taurus star-forming region. We derive the spectral type and Halpha equivalent width of each component. Complementing these results with those of Monin et al. (1999) yields a sample of 14 binaries and one triple system, with resolved spectroscopy and/or near-infrared photometry. We find that mixed binaries (CTTS+WTTS) are rare, representing only 15-20% of the systems in the separation range of 0.8" to 3''. Supplementing these results with those of Hartigan et al. (1994) and Prato & Simon (1997), we show that the trend of binary TTS to be twins holds to separations up to 13''. This is unlikely to be the result of random pairing, and confirms previous results that both stars in young binaries accrete over the same time span. In binary systems where both stars are still accreting, our measurements show that the most massive star is usually the component with the largest accretion rate by up to a factor of 10, as determined from the Halpha luminosity.

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arXiv1999

Low-mass binaries in the young cluster IC 348: implications for binary formation and evolution

We report on a near-infrared adaptive optics survey of a sample of 66 low-mass members of the pre-main sequence stellar cluster IC 348. We find 12 binary systems in the separation range 0.1-8.0 arcsec. An estimate of the number of faint undetected companions is derived, before we evaluate the binary frequency in this cluster. In the orbital period range log P=5.0-7.9 days, the binary fraction in IC 348 is 19+/-5 %.This is similar to the values correspondings to G- and M-dwarfs populations in the solar neigbourhood. Substellar companions are found to be rare, or even missing, as companions of low-mass stars in the separation range we surveyed. Also, the mass ratio distribution is not peaked at q=1. We do not find any evidence for an evolution of the binary frequency with age within the age spread of the cluster of about 10 Myr. We conclude that there is no temporal evolution of the binary fraction between a few Myrs after the formation process, the zero-age main sequence and the field population. We find instead a trend for the binary fraction to be inversely correlated with stellar density, with only loose associations exhibiting an excess of binaries. Either all star-forming regions initially host a large number of binaries, which is subsequently reduced only in dense clusters on a timescale of less than 1 Myr due to numerous gravitational encounters, or specific initial conditions in the parental molecular clouds impact on the fragmentation process leading to intrinsically different binary fractions.

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arXiv1998

Binary fraction in low-mass star forming regions: a reexamination of the possible excesses and implications

Various surveys of low-mass binaries in star forming regions have been performed in recent years. They reached opposite conclusions concerning possible binary excesses in some of these associations. I develop a consistent method to reanalyze all these studies, so that I can compare all data consistently, and understand the previous findings. I also report the detection of five new companions to Taurus members. It appears that binary fraction in Taurus exceeds the main sequence value by a factor of 1.7 in the range 4-2000 AU. The companion star fraction in this separation range is the same as the overall main sequence fraction. Ophiuchus, Chameleon, and possibly Lupus show similar excesses, although with lower confidence levels. Binaries in Ophiuchus seem to have larger flux ratios (towards faint companions) than in Taurus. It appears very unlikely that all very young star forming regions have binary excesses. The binary fraction seems to be established after $\sim$ 1 Myr, but the precise nature of the difference between various regions is still unclear (overall binary fraction, orbital period distribution). It is not currently possible to put constraints on the binary formation models: higher angular resolution and larger sample sizes will be required.

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