11 research outputs found
Near Infrared Spectroscopic Monitoring of EXor variables: First Results
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.Comment: To be published in Ap
The Spitzer survey of interstellar clouds in the Gould Belt. II. The Cepheus Flare observed with IRAC and MIPS
We present Spitzer IRAC (~2 deg^2) and MIPS (~8 deg^2) observations of the
Cepheus Flare which is associated with the Gould Belt, at an approximate
distance of ~300 pc. Around 6500 sources are detected in all four IRAC bands,
of which ~900 have MIPS 24 micron detections. We identify 133 YSO candidates
using color-magnitude diagram techniques, a large number of the YSO candidates
are associated with the NGC 7023 reflection nebula. Cross identifications were
made with the Guide Star Catalog II and the IRAS Faint Source Catalog, and
spectral energy distributions (SED) were constructed. SED modeling was
conducted to estimate the degree of infrared excess. It was found that a large
majority of disks were optically thick accreting disks, suggesting that there
has been little disk evolution in these sources. Nearest-neighbor clustering
analysis identified four small protostellar groups (L1228, L1228N, L1251A, and
L1251B) with 5-15 members each and the larger NGC 7023 association with 32 YSO
members. The star formation efficiency for cores with clusters of protostars
and for those without clusters was found to be ~8% and ~1% respectively. The
cores L1155, L1241, and L1247 are confirmed to be starless down to our
luminosity limit of L_bol=0.06 L_sol.Comment: Submitted to ApJSS. 20 figures, 110 page