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T Tau project

SBL
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Joined: 2010-08-08

Hi,
I want to monitor (AAVSONet) some T Tau stars (Tau-Aur region) this and next season and do some spectroscopy next winter.

T Tau
DF Tau has DG Tau (also T Tau star) in the same FOV
VY Tau varying between CTTS and WTTS
V773 Tau only WTTS with sufficient low magn. for spectroscopy
SU Aur large magn. range and spectral range

any suggestions or comments on:
- choice of target stars
- filters to use: BVRI or Sloan?
- anything else
are welcome

thanks,

Bart Staels
SBL

T Tau project
HQA
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Joined: 2010-05-10

Hi Bart,

T Tau variables are interesting to study.  As young stellar objects, they tend to have chaotic variation as they have not stabilized on the Main Sequence, are adjusting their structure, and generally have clouds of gas and dust in their environment.  I'd expect more eclipsers than have been discovered and periods of quasi-periodic oscillations.  Certainly spectroscopy is the main way to study these stars, as the radial velocity and strength of lines tells you a lot about what is emitting or absorbing, and whether it is gas that is infalling onto the newly formed star.  As you say, though, most of these stars are too faint for good high resolution spectroscopy with amateur sized telescopes.  As they are just breaking out of their "cocoon", they tend to illuminate the surrounding gas, producing visible nebulosity.

T Tau itself hasn't gotten a lot of attention from the CCD crowd, and deserves more.  For all TTau objects, multifilter observations are highly useful to help discern where the variations are coming from (you can tell whether a dip is the same depth at all wavelengths, for example).  I'd also see what timescales are involved, by trying a few time series nights as well as nightly monitoring.  High precision is recommended - try to get at least S/N=100 per observation.

The existing datasets on TTau objects are almost all BVRI, so it is probably best to stick with Johnson/Cousins for now.  R-band includes Halpha, so you will have more trouble interpreting variations in that band.  The stars you suggest are good ones, but one thing to watch is that TTau objects tend to be clustered, and you need to be careful that your comparison stars are constant and not variables in their own right.  I remember observing V410 Tau for a campaign, and having to use a 23arcmin field with the variable in one corner and the nearest good comparison in the opposing corner.

The 24-inch telescopes of AAVSOnet should be large enough for spectroscopy of the brighter TTau objects.  You might also consider W28, which has an Halpha filter and a nearby continuum filter, and monitor the objects at Halpha - a poor man's spectrograph.

Arne

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484