arXiv subjects

M. Simon

Publications and source records attributed to M. Simon.

95 records · Page 6Linked to original sources

arXiv2001

A Dynamical Mass Constraint for Pre-Main-Sequence Evolutionary Tracks: The Binary NTT 045251+3016

We present an astrometric/spectroscopic orbital solution for the pre-main-sequence binary NTT 045251+3016. Our measurements for the primary and secondary masses are 1.45 +/- 0.19 M_sun and 0.81 +/- 0.09 M_sun, respectively, and 145 +/- 8 pc for the distance of the system, consistent with prior estimates for the Taurus-Auriga star-forming region. The evolutionary tracks of D'Antona & Mazzitelli (1997), Baraffe et al. (1998), and Palla & Stahler (1999) are tested against these dynamical mass measurements. Due to the intrinsic color/T_eff variation within the K5 spectral class, each pre-main-sequence model provides a mass range for the primary. The theoretical mass range derived from the Baraffe et al. (1998) tracks that use a mixing length parameter alpha=1.0 is closest to our measured primary mass, deviating between 1.3 and 1.6 sigma. The set of Baraffe et al. (1998) tracks that use alpha=1.9 deviate between 1.6 and 2.1 sigma from our measured primary mass. The mass range given by the Palla & Stahler (1999) tracks for the primary star deviate between 1.6 and 2.9 sigma. The D'Antona & Mazzitelli (1997) tracks give a mass range that deviates by at least 3.0 sigma from our derived primary mass, strongly suggesting that these tracks are inconsistent with our observation. Observations of the secondary are less constraining than those of the primary, but the deviations between the dynamical mass of the secondary and the mass inferred for the secondary from the various pre-main-sequence tracks mirror the deviations of the primary star. All of the pre-main-sequence tracks are consistent with coevality of the components of NTT 045251+3016.

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arXiv2001

The Variability of T Tau, RY Tau and RW Aur from 1899 to 1952

We present the historical light curve of T Tau derived from photographic plates in the Harvard College Observatory archives. We find that the optical light of T Tau varied by 2-3 (or more) magnitudes on time scales as short as a month prior to ~1917, consistent with the results of Lozinskii (1949). Extreme light fluctuations of greater than 2 magnitudes abruptly ceased in the late 1910's and, to the best of our knowledge, have not repeated since this time. We compare the observed light variations of T Tau to the T Tauri stars RY Tau and RW Aur, whose light curves we also constructed from inspection of the archival plates. We find that variable extinction along the line of sight to the star is the most likely explanation for the observed light fluctuation of T Tau during the early part of the 20th century.

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arXiv2001

The near-infrared and ice-band variability of Haro 6-10

We have monitored the angularly resolved near infrared and 3.1 micron ice-band flux of the components of the young binary Haro 6-10 on 23 occasions during the years 1988 to 2000. Our observations reveal that both the visible star Haro 6-10 (Haro 6-10S) and its infrared companion (Haro 6-10N) show significant variation in flux on time scales as short as a month. The substantial flux decrease of Haro 6-10S over the last four years carries the reddening signature of increased extinction. However, a comparable K-band flux increase observed in the IRC is associated with a dimming in the H-band and cannot be explained by lower extinction. Absorption in the 3.1 micron water-ice feature was always greater towards the IRC during our observations, indicating a larger amount of obscuring material along its line of sight. We detect variability in the ice-band absorption towards Haro 6-10S and Haro 6-10N, significant at the 3.5 sigma and 2.0 sigma levels, respectively.

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arXiv2001

Evidence for Extinction and Accretion Variability in T Tau S

We present angularly resolved spectra of T Tau North and South in the 3 micron water ice feature and K-band. Most of the water ice absorption lies along the line of sight toward T Tau South, confirming that it is viewed through stronger extinction. A decrease in ice-band absorption toward T Tau S between December 1998 and January 2000, significant at the 2 sigma level, was associated with an increase in its near infrared flux. Br gamma emission is detected in T Tau North and South and H_{2} (2.12 micron) emission only toward T Tau South, consistent with previous studies of infrared companions to T Tauri stars. Our results suggest that the near IR variability of T Tau S is probably caused by both variations in accretion rate and variable extinction along the line of sight.

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arXiv2000

Dynamical Masses of T Tauri Stars and Calibration of PMS Evolution

We have used the high sensitivity and resolution of the IRAM interferometer to produce sub-arcsecond 12CO 2-1 images of 9 protoplanetary disks surrounding T Tauri stars in the Taurus-Auriga cloud (7 singles and 2 binaries). The images demonstrate the disks are in Keplerian rotation around their central stars. Using the least square fit method described in Guilloteau and Dutrey (1998), we derive the disk properties, in particular its inclination angle and rotation velocity, hence the dynamical mass. Since the disk mass is usually small, this is a direct measurement of the stellar mass. Typically, we reach an internal precision of 10% in the determinations of stellar mass. The over-all accuracy is limited by the uncertainty in the distance to a specific star. In a distance independent way, we compare the derived masses with theoretical tracks of pre-main-sequence evolution. Combined with the mean distance to the Taurus region (140 pc), for stars with mass close to 1 Msun, our results tend to favor the tracks with cooler photospheres (higher masses for a given spectral type). We find that in UZ Tau E the disk and the spectroscopic binary orbit appear to have different inclinations.

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