Observation request: T Tau early in January

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Observation request: T Tau early in January

Postby Hans Moritz Guenther » Mon Dec 15, 2014 4:56 pm

Hi,

I am an astronomer at the Harvard-Smithsonian Center for Astrophysics right now and I want to ask for your help with an observing project:

We are working on classical T Tauri stars, trying to understand how exactly the disks around those stars interact with the star itself. The circumstellar disk in these objects does not reach down to the central star (the inner hole can be resolved in radio observations), but mass from the disk can be funneled into a few accretion spots on the star. These accretion funnels are visible in H alpha and the H alpha equivalent width is a good indicator for the rate of accretion from the disk onto the star. The accretion spots itself become very hot, several million degrees, and shine in X-rays.

We applied for use of the Chandra X-ray telescope to observe T Tau, the namegiver of the class of T Tauri stars to get a spectrum of the X-ray emission from the accretion spots. It would be really useful to also know what the H alpha line is doing at that time. In classical T Tauri stars the H alpha line is typically very wide (about 500 km/s) and in emission. T Tau has V = 9.3 mag, so a low- or medium resolution spectrum does not require an exceptionally large telescope if you expose for e.g. an hour. While it's always helpful to know more details :) , all we really need is the equivalent width of the H alpha line.

We'd love to get about one spectrum per night for a couple of days before and after and as much as we can during the Chandra observation. Chandra will observe for over 30 hours, so we need telescopes on more than one site. We have a 1.2 m telescope in Mexico, that will observe from there (weather permitting), but we need support in Europe and if some of you are in America to back us up in case the observations from Mexico fail (they did last time we tried something similar) that would be fabulous.

Observations with Chandra are scheduled not too long in advance due to the way the orbit of the satellite works. T Tau is currently in the long-term schedule for observations some time between 29-Dec-2014 and 12-Jan-2015 (http://cxc.harvard.edu/target_lists/longsched.html), the exact data will only be decided about one week in advance.
The short term schedule is here, but T Tau is not on it yet: http://cxc.harvard.edu/target_lists/stscheds/
I will post an update here when the date is set.

People on this forum tried to help me with a similar science project before (http://www.spectro-aras.com/forum/viewtopic.php?f=5&t=246), but unfortunately Europe was covered in dense clouds during the time of the X-ray observations. However, there are sample observations in http://www.spectro-aras.com/forum/viewtopic.php?f=5&t=246, that list setup and exposure time for the observations of SU Aur, which has almost the same magnitude as T Tau.

Cheers,
Moritz
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Re: Observation request: T Tau early in January

Postby Hans Moritz Guenther » Mon Dec 15, 2014 5:26 pm

To give you an idea how wide H alpha is I attach a spectrum that we took a while ago (2014 Nov 10) with a 1.2m mirror and 180 seconds of exposure time.
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Ha_spec_TTau.png
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Re: Observation request: T Tau early in January

Postby Paolo Berardi » Sun Dec 28, 2014 11:56 am

It is a very interesting activity! I do not own a big telescope and I would like to ask if a spectrum like the one attached may be useful for the purpose.

Image

Resolving power is about 6000. It was obtained with a Lhires III spectrograph equipped with a 1200 l/mm grating, 31 microns slit and a 9.25 inch telescope aperture. Total exposure 80 minutes.

I can also use a 2400 l/mm (R~15000) with which, using similar exposure time, I clearly would get a lower SNR. I wonder which is better (when possible I could take a spectrum with this configuration).

Profile in standard FITS is enclosed to allow a better evaluation.

Thank you very much!

Paolo Berardi
Attachments
_ttau_20141221_920.zip
FITS profile
(9.58 KiB) Downloaded 198 times
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Re: Observation request: T Tau early in January

Postby Christian Buil » Sun Dec 28, 2014 3:46 pm

Here an observation of T Tauri star taken in high resolution mode the 21 Dec 2014 with a 28 cm
Schmidt-Cassegrain telescope and the VHIRES-MO (R = 50000) spectrograph
(see http://www.astrosurf.com/buil/vhires/demo3.htm).

Halpha profile:

Image

Observed oxygen line at 6300 A (star OI airglow ?):

Image

Part of the 2D spectrum (50 minutes exposure on this 9.3 mag. star):

Image

(see also topic http://www.spectro-aras.com/forum/viewtopic.php?f=6&t=1042&p=4629#p4629).

Medium and... high resolution are possible on this target. Observations are welcome!
(we can prepare an ARAS page for collect spectra).

Christian B
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Re: Observation request: T Tau early in January

Postby Christian Buil » Sun Dec 28, 2014 4:48 pm

A MEDRES spectrum of T Tauri the 21/12/2013 (same date as VHIRES spectrum) - C11 + Fiber link and 300 l/mm grating spectrograph - R = 1800,
exposure 3 x 600 seconds):

Image

Image

Compare with Paolo spectrum also.

Christian B
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Re: Observation request: T Tau early in January

Postby Robin Leadbeater » Mon Dec 29, 2014 2:51 pm

Hans Moritz Guenther wrote:The short term schedule is here, but T Tau is not on it yet: http://cxc.harvard.edu/target_lists/stscheds/
I will post an update here when the date is set.


I See T Tau is now on the list for 1st Jan

T Tau 2015:001:13:25:10.407

Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
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Re: Observation request: T Tau early in January

Postby Tim Lester » Tue Dec 30, 2014 5:28 pm

T Tau for Dec 30th (R = 8800)

Image

Where are the spectra being collected?
Hope it is clear on the 1st (the forcast is not good for me).

Tim
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Chandra time is set

Postby Hans Moritz Guenther » Tue Dec 30, 2014 9:13 pm

Chandra has now released the schedule (OK, they may have done so two or three days ago, but I was busy with Christmas and moving into a new apartment):
The Chandra observation will be

Start time: 2015:001:13:25:25.870 (1. Jan 2015 13:25 UT)

Stop time 2015:003:01:15:25.870 (3. Jan 2015 1:15 UT)

(all times in UT).

Any Halpha spectrum around that time would be great!

Moritz
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Spectra in this thread

Postby Hans Moritz Guenther » Tue Dec 30, 2014 9:25 pm

Hi,

looking at all the spectra you already posted in this thread, they look fantastic, almost too good!
Classical T Tauri stars tend to be time variable on time scales below one hour. With Chandra, we get the data with a time resolution of just a few seconds. If nothing interesting happens, we can always add up the data for longer time intervals later.

Similarly, it would probably the best for us, if you can take short (ideally < 15 min) exposures.

When we looked with Chandra at TW Hya (a CTTS that has much less mass then T Tau, but is otherwise similar) a few years ago, TW Hya showed a sudden flare in X-rays that lasted less than one hour. The question now is: Is this a magnetic flare similar to solar activity or is this a large clump of mass that falls onto the star? If it is solar activity, H alpha will change, but stay relatively narrow. On the other hand, if it is a large clump of mass that falls on the accretion shock, the Halpha line will become much wider and much brighter.

For this question, the quality of the spectrum is not very important - all we need to measure is the H alpha equivalent width (it's always nice to have the line profile, sure, but that's not as important). On the other hand, we need at least one spectrum before the flare and a second spectrum during the flare. If we only had one spectrum with a very long exposure time (even if the signal is fantastic) we could not say if the H alpha line changes at all during the flare.

Thus, I want to encourage you to take short spectra, even if the quality is not as good.

Let's hope for clear skies!

[Edited: Fixed typo I had overlooked.]
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Re: Observation request: T Tau early in January

Postby Robin Leadbeater » Wed Dec 31, 2014 5:39 pm

Some spectra from the last two nights (LHIRES 1200 l/mm R~5500)
These are combined exposures. The individual spectra are 5 min exposure but the SNR of these is rather low at ~15 at best in the continuum.

I have seen very fast large changes in T Tauri stars before in very low resolution spectra, even within 5 minutes
http://www.threehillsobservatory.co.uk/ ... ra_42a.htm

Unfortunately the weather forecast is not good here either

Robin
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