HST/TESS observations of TW Hya 3/7 - 4/9 2021

Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 02/19/2021 - 17:19

Part II of the ODYSSEUS pre-main sequence star program starts next month. ODYSSEUS is an international collaborative campaign to understand the processes involved in the formation of low mass stars, their circumstellar disks, and their planets, via the time-variability of these systems.


The HST will monitor the 10 million year old K7 pre-main sequence star TW Hya intensively, obtaining 12 sets of ultra-violet spectra spread over about 13 days, 7-19 March, simultaneously with TESS observations.
TESS will observe this part of the sky nearly continuously for 27 days, from 7 March through 2 April, with a 10 minute cadence. TESS data, both in terms of length of coverage and data quality, cannot be matched from the ground, but TESS is a single channel photometer operating in the red. We need ground-based optical photometry to place the TESS magnitudes in context.
- Are stellar variations due to enhanced accretion events or long-lived flares, which case the star to become bluer, or
- are they due to variable circumstellar extinction, in which case the star will become redder, or
- are they due to obscuration of the photosphere by optically-thick irregularities in the circumstellar disk, in which the color should not change?
Changes in extinction in particular are important for interpreting the UV spectra, which are very sensitive to the absorption.

TW Hya is at 11:01:51.9 -34:42:17.0 (J2000).
It is fairly bright, with a mean V ~ 11, and a historical range from 10.6 to 11.3 (from VSX).
The typical day-to-day range of variability is +/- 0.1 mag.
I seek to extract colors accurate to better than 2% (0.02 mag), which requires CCD photometry accurate to better the 0.01 mag.

If you can reach this southern target, please add it to your observing list from 6 March through 2 April.
- Highest priority will be during the HST observations, but those exact times are not known yet.
- Next highest priority are nightly observations 6 through 19 March inclusive, spanning the time of the HST observations. No more than one observation is needed per night.
- Lower priority would be from 20 March through 2 April, when only TESS is on the target.
Please observe in 4 bands (B,V and either Cousins RI (preferred) or Sloan ri.)

When I learn exactly when the HST observations will be scheduled, I will provide that information. But contemporaneous photometry more than suffices for our purposes.

Please upload any data you get to the AAVSO database. Thanks in advance for your contributions to this campaign.

 

Affiliation
American Association of Variable Star Observers (AAVSO)
TW Hya to be observed with HST and TESS

AAVSO Alert Notice 731 announces a campaign on the T Tau star TW Hya. Please see the notice for details and observing instructions.

There are threads for this campaign under the following forums:

- Campaigns and Observation Reports: https://www.aavso.org/hsttess-observations-tw-hya-37-42-2021-01
- Young Stellar Objects (YSO): https://www.aavso.org/hsttess-observations-tw-hya-37-42-2021

Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomer and by HQ. Join in the discussion or ask questions there!

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ

Affiliation
American Association of Variable Star Observers (AAVSO)
HST schedule for TW Hya - observations needed

AAVSO Alert Notice 733 gives the schedule of HST observing times for the T Tau star TW Hya. The first observations are scheduled for 2021 March 09 UT. Please see the notice for details and observing instructions. This campaign was announced in Alert Notice 731.

There are threads for this campaign under the following forums:

- Campaigns and Observation Reports: https://www.aavso.org/hsttess-observations-tw-hya-37-42-2021-01
- Young Stellar Objects (YSO): https://www.aavso.org/hsttess-observations-tw-hya-37-42-2021

Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomer and by HQ. Join in the discussion or ask questions there!

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ

Affiliation
American Association of Variable Star Observers (AAVSO)
HST and TW Hya / Alert Notice 733

Thanks to all of you who have been obtaining data.

Unfortunately the HST went into safe mode on March 7, which canceled the planned March 7-19 observations.

The HST is functioning again, and the TW Hya observations are now being rescheduled between March 22 and April 8. When I have more information, I'll post it.

In the mean time, please keep observing. The TESS observations are continuing as planned, as is my high-dispersion spectroscopic monitoring.

Thanks, and clear skies.

Fred

Affiliation
American Association of Variable Star Observers (AAVSO)
HST and TW Hya Scheduling Update

Hi all,

Thanks again to those of you who have been collecting and reporting data. Over the past month TW Hya has varied by over 1 mag at B and lesser amounts at VRI, on timescales of a few days.

The revised HST schedule is now out. There will be 12 observations in all. The first 7 observation times (in UT), March 29-April 4, are:

 1:  Start time: 29 Mar 2021 16:11:22               End time: 29 Mar 2021 17:04:24
 2:  Start time: 30 Mar 2021 16:00:47               End time: 30 Mar 2021 16:53:49
 3:  Start time: 31 Mar 2021 09:29:01               End time: 31 Mar 2021 10:22:03
 4:  Start time: 01 Apr 2021 10:53:42               End time: 01 Apr 2021 11:46:44
 5:  Start time: 02 Apr 2021 12:18:21               End time: 02 Apr 2021 13:11:23
 6:  Start time: 03 Apr 2021 04:11:15               End time: 03 Apr 2021 05:04:17
 7:  Start time: 04 Apr 2021 07:11:10               End time: 04 Apr 2021 08:04:12

Observations 8-12 will be scheduled April 5-9.

Depending on your longitude, if you can get observations during the times of the HST observations, they will be most valuable.

The first 4 observations will be simultaneous with TESS observations. During those nights it is most important to get good colors. After that TESS moves on, and your data will provide the best photometric record of what the star is doing, so a few observations over the course of the night would be valuable.

Thanks, and clear skies,

Fred

 

Affiliation
American Association of Variable Star Observers (AAVSO)
HST and TW Hya Final Scheduling Update - April 3-8 UT

Hi all,

Thanks again to those of you who have been collecting and reporting data. Over the past month TW Hya has varied by over 1 mag at B and lesser amounts at VRI, on timescales of a few days.

The final HST schedule is now out. There will be 12 observations in all. The remaining observation times (in UT), through April 8, are:

 
 6:  Start time: 03 Apr 2021 04:11:15               End time: 03 Apr 2021 05:04:17
 7:  Start time: 04 Apr 2021 07:11:10               End time: 04 Apr 2021 08:04:12

 8:  Start time: 05 Apr 2021 03:49:55               End time: 05 Apr 2021 04:42:57
 9:  Start time: 05 Apr 2021 13:21:38               End time: 05 Apr 2021 14:14:40
10: Start time: 06 Apr 2021 13:10:56               End time: 06 Apr 2021 14:03:58
11: Start time: 07 Apr 2021 13:00:14               End time: 07 Apr 2021 13:53:16
12: Start time: 08 Apr 2021 12:52:27               End time: 08 Apr 2021 13:45:29
 

Depending on your longitude, if you can get observations during the times of the HST observations, they will be most valuable. But all observations are important, since the TESS observations ended on April 2. BVRI (or ri) filter photometry is most useful.

Thanks, and clear skies,

Fred

Affiliation
American Association of Variable Star Observers (AAVSO)
TW Hya - final HST observations - Alert Notice 737

AAVSO Alert Notice 737 gives the dates/times of the final set of upcoming HST observations of TW Hya. Please see the Notice for details and observing instructions.

There are threads for this campaign under the following forums:

- Campaigns and Observation Reports: https://www.aavso.org/hsttess-observations-tw-hya-37-42-2021-01
- Young Stellar Objects (YSO): https://www.aavso.org/hsttess-observations-tw-hya-37-42-2021

Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomer and by HQ. Join in the discussion or ask questions there!

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ