spectro-aras.com

Via an alert notice of AAVSO, Darryl Sergison (University of Exeter) request spectroscopy of 3 T Tauri stars : RY Tau - DN Tau - DR Tau

Currently the magnitudes of these stars are :

RY Tau Mag V = 10.2
DN tau Mag Vis = 12.4
DR Tau Mag Vis = 12



Alert Notice 473: T Tauri stars observing campaign

November 6, 2012: Darryl Sergison (University of Exeter) has requested AAVSO assistance with a campaign he is organizing on six T Tauri stars. He writes: "In Autumn 2013 I [and my PhD supervisor Tim Naylor of Exeter University are] undertaking a new study into the nature of pre-main-sequence low mass stars, using time series optical spectroscopy and UV-Visual-IR photometry...to build a clearer picture of the environment around young solar-type stars and characterise their various disc, accretion, and outflow structures.

"This study offers a great opportunity for professional-amateur collaboration as the objects (with V magnitudes of 10 - 13) are well within the reach of photometry by small telescopes. Amateur observations are uniquely useful to us in the study of chaotically variable young stars as they offer crucial datapoints in the lightcurve between observations made by professional telescopes.

"We would be very keen to recruit(!) AAVSO observers who are interested in being part of this study and able to contribute visual or (V and Rc band) filtered CCD photometry. All contributing observers will be acknowledged in the published papers, significant contributors may also be co-authors. I do have one spare 1.25" V band filter that I could lend to any interested observer who may wish to borrow it for the duration of this programme. [If you are interested in borrowing it please email eowaagen@aavso.org].

"In preparation for the main data collection next autumn, we would like to start monitoring targets immediately. The first 3 targets that we will be studying are RY Tau, DN Tau, and DR Tau [the other 3 targets will be announced later]...

"As far as observations go, almost anything is useful. We are hoping to investigate periodicity for a range of phenomena on timescales of months to hours, so visual estimates ranging from monthly to twice in a night would be great.

"Filtered CCD measurements in any of B, V, Ic, or Rc would be great, again low cadence is useful, higher cadence (hourly or long time series) is better! Unfiltered is probably of less use to us due to the difficulties with system response and changing air-mass.

"Spectroscopy would be very welcome, particularly around H-alpha (6563Å) if the resolution is greater than a few thousand. Alternatively, low resolution right across the optical would be great (for example with a diffraction grating in the converging beam), particularly if a nearby main sequence star of similar spectral type can be captured at a similar time and air-mass so that we can characterise the system and atmosphere response at the time of the observation."

Coordinates (2000) Range B-V
RY Tau RA 04 21 57.41 Dec +28 26 35.6 9.3-13.0 p 1.0
DN Tau RA 04 35 27.38 Dec +24 14 58.9 11.5-14.7 p 1.4
DR Tau RA 04 47 06.22 Dec +16 58 42.8 10.5-16 B 1.2

Reference stars for atmospheric and instrumental response :


7 November 2012: Further to AAVSO Alert Notice 473 (www.aavso.org/aavso alert-notice/473), Principal Investigator Darryl Sergison (University of Exeter) requests that spectroscopists planning to observe the targets RY Tau, DN Tau, and/or DR Tau image the corresponding telluric standards below at the same time:

Telluric standard for RY Tau
HD 283567 B9 Vmag = 10.38 RA 04 20 33.072 Dec +28 39 08.55

Telluric standard for DN Tau
HD 284571 A0 Vmag = 9.71 RA 04 37 46.253 Dec +24 02 45.93

Telluric standard for DR Tau
HD 286036 A0 Vmag = 10.54 RA 04 46 26.684 Dec +15 59 45.47

Imaging these objects at the same time as the targets will enable the removal of the effects of system response and atmospheric absorption.

Coordinates (2000)
RY Tau RA 04 21 57.41 Dec +28 26 35.6
DN Tau RA 04 35 27.38 Dec +24 14 58.9
DR Tau RA 04 47 06.22 Dec +16 58 42.8

RY Tau last night, under poor atmospheric conditions (fog)



See also Ha profile obtained by Thierry Garrel :



François Teyssier

Francois Teyssier wrote:RY Tau last night, under poor atmospheric conditions (fog)

Same conditions here last night. I tried AZ Cas in the blue but it was hopeless

Did you try using the suggested Telluric standard?

I have been talking to Darryl about his idea of using the Star Analyser or similar. He is mainly looking for a way to do photometry with it so extinction correction would be important. I think multi filter photometry would be easier and more accurate but it could be useful to separate the effect of changes in the lines compared with the continuum (particularly in the Rc channel for example)

Cheers
Robin

Hi Robin - I am going to try to do both BVRc Photometry and the Lisa for the spectroscopy at the same time using a 140mm for the photometry and my 300mm for the spectroscopy. I have been interested in trying to do both for a while. Unfortunatly one of my cameras has a fault at the moment so I can't get started but anyway the weather has been just cloud and rain.

Regards Andrew

Hello Robin and Andrew,

I didn't use the standart suggested by Darryl Sergison ; it should have been time consuming according to the weather conditions (about 1 hour)
I choosed HD 29646 a mag 5.8, A2V star whose declination is the same as RY Tau one.

I suggested Darril Sergison to choose brighter standart stars (mag 5-6) in order to save observation time (and, I think, better intrumental response)
Waiting for his response.

Very good idea, Andrew, to get spectrum AND luminosity.
Waiting for your results.

Best regards

François

Here spectra of DY Tau, DN Tau and DR Tau taken with moderate resolution
(R=2400). Lhires III 600 l/mm on a Celestron 9 telescope. 35 microns slit.
Atik460EX CCD camera (binning 2x2) :



Full sized plot: http://www.astrosurf.com/buil/campaign/ ... _compa.png

Hazy night from my Castanet-Tolosan observtory. Better result is expected...

Note on the same profile the Halpha line, the Na doublet and yellow He line
(in emission on DN Tau and DT Tau star spectra)

The setup is relatively confortable for capture V=12 mag. star spectra.

Christian B

I'm quite keen to try the more southern of these stars as well. This will be DR Tau but it will have to wait a month or so to make it high enough in the sky in the late evening (some of us have to work so need to sleep after midnight )
I can easily take BVRI photometry at the same time as a LISA spectra through my 2 side by side mounted scopes.
I'm not sure what to do about the telluric standards though. I need a standard at the same airmass and probably a standard spectra to compare it to. I currently use the pickles standards rather than an actual spectra from the HD star being observed due to not having the actual spectra for any of the southern HD stars I observe.
If a particular HD star is decided to use as telluric standards for each variable then should there also be a standard spectra used as well?

Cheers

Terry

Hi,

Aspect of DR Tau spectrum taken with a LISA spectrograph on C9 telescope and 14 x 300 seconds exposure:



Note the ultraviolet CaII in emission, a rare phenonomen.

Christian B

Some resultats of the pre-campaign.

First, fast changes in the spectrum of RY Tau observed by Thierry Garrel (eShel spectrograph) and
myself (Lhires III spectrograph at the highest resolution) in just one week. The signal to noise ratio is similar between
the two spectra for a quite different instrumentation:



A summary showing all resolutions covered by spectrographs (missing StarAnalyser spectrum):



The star RY Tau can be captured with a resolution of 16000 (Lhires III 2400) with a little care,
but it will be difficult for DN Tau and DR Tau, a little faintest, with 235 mm - 280 mm class telescopes.
A Lhires III 1200 l / mm (R = 7500) is probably more comfortable. All these objects are, however, fairly easy with a
Lhires III 600 l / mm (R = 2500), also with a telescope of 200 mm diameter probably.

Thierry Garrel demonstrate the efficiency with an eShel + C14 on RY Tau.

There is no problem with LISA for stars at magnitude 12 (remember, this spectrograph can detect V=16-17 on a
0.28m telescope - but only with a resolution of R = 800 to 1000 of course).

Photometric consistency is shown on two independent observations performed in two different nights on DR Tau (here a LISA spectrograph):



For my observations I used arbitrarily HD29646 as a reference star (spectral type A2V and bright). The next
plot shows typical spectrum of the star acquired with a LISA spectrograph and comparison with Pickles synthetic model of a A2V star:



The processing procedure is standard under ISIS (bias subtraction, thermal signal subtraction, flat-field corrected by using white lamp,
sky removing, geometric corrections, optimal profile extraction, wavelength calibration, division by instrumental response, ...).

Note that HD29646 spectrum only serves to evaluate smoothed instrumental response (including atmospheric transmission) i.e. a low frequency
wavelength evolution of instrument efficiency + atmophere transmission. Areas where H2O telluric lines are present (around Halpha and
around the sodium doublet) are cleared by spline interpolation in the actual instrumental response definition.

If necessary, the telluric lines are removed only in a final step by fitting a synthetic H2O spectra (ISIS exploit data of
atmopsheric GEISA database).

Actually tellutric are not automatically removed during standard processing pipeline because some programs (monitoring of Be stars, Meudon
observatory, for example) impose to keep the telluric lines in the processed spectra (they can serve latter to improve spectral
calibration and it is also proved that telluric lines removal procedure requires a little care).

Christian B

Hello,

I just would like to know reference stars you have choose for these 3 stars.
If I can understand, the three reference stars must be near T Tau and, in order to compute atmospheric absorption, must be in the NOAO of the database of ISIS. Is it good ?
Star of mag 10 is faint for HR spectra and so a good result of atmospheric absorption. I know it is not very important to do spectrum of reference star for HR but I just would like to know if you have took brighter reference star ?

Stephane