Near Infrared Spectroscopic Monitoring of EXor variables: First Results

TL;DR

This study presents initial near-infrared spectroscopic observations of EXor variables, revealing diverse emission features, wind and accretion signatures, and correlations between continuum variability and spectral line changes in young stellar objects.

Contribution

First near-IR spectroscopic monitoring of EXor variables, linking spectral features with accretion and wind processes, and analyzing variability stages in pre-main sequence stars.

Findings

Emission features dominated by HI recombination lines.

Mass loss rates estimated between (2-10)x10^(-8) M_sun/yr.

CO features vary with activity stage, indicating different emission regions.

Abstract

We present low resolution (R approximately 250) spectroscopy in the near-IR (0.8 to 2.5um) of the EXor variables. These are the initial results (obtained during the period 2007-2008) from a long term photometric and spectroscopic program aimed to study the variability in the accretion processes of pre-Main Sequence (PMS) stars, by correlating the continuum fluctuations with the spectroscopical properties. Eight sources have been observed in different epochs, for a total of 25 acquired spectra. EXor spectra show a wide variety of emission features dominated by HI recombination (Paschen and Brackett series). We have investigated whether line and continuum variability could be due to a variable extinction, but such hypothesis is applicable only to the peculiar source PV Cep. By comparing the observed spectra with a wind model, mass loss rates in the range (2-10)x10^(-8) M_sun} yr^(-1) are derived, along with other wind parameters. Consistent results are also obtained by assuming that HI lines are due to accretion. CO overtone is also detected in the majority of the sources both in absorption and in emission. It appears to come from regions more compact than winds, likely the stellar photosphere (when in absorption) and the circumstellar disk (when in emission). NaI and CaI IR lines behave as the CO does, thus they are thought to arise in the same locations. For some targets multiple spectra correspond to different activity stages of the source. Those exhibiting the largest continuum variation at 2um (DeltaK > 1 mag) present a significant line flux fading during the continuum declining phases. In particular, CO absorption (emission) appears associated to inactive (active) stages, respectively.