ODYSSEUS IV: HST/XMM observations of RU Lup nd BP Tau

Part IV of the ODYSSEUS pre-main sequence star program starts this 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 pre-main sequence stars RU Lup and BP Tau, obtaining 12 sets of ultra-violet spectra spread over roughly three rotation periods for each star. The window for RU Lup is August 10-20; the window for BP Tau is August 20 - September 12. Five of the RU Lup observations will be simultaneous with X-ray
observations from XMM. Neither target will be observed simultaneously with TESS, so ground-based observations are critical if we are to place the HST and XMM
observations in a long-term context.

Thank you for your contributions to the first 3 parts of the ODYSSEUS campaign. Your participation in this campaign is a big part of its success.

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

I. RU Lupi
Position: 15 56 42.31 -37 49 15.5 (J2000).
Magnitude: V~9.6
This is a bright, highly active classical T Tauri star in the Lupus star formation region. The rotation period is about 3.7 days. The system is almost pole-on, so stochastic variability dominates over rotational modulation. The VSX catalog reports it as faint as V=12.9, but it is generally closer to its brightest level. The TESS data from 2019 shown peak-to-peak variations of 0.8 mag.
Please try to get 1% BVRI CCD photometry (0.01 mag precision), we we can determine colors to 2% or better.

The current HST schedule is:
Date                   DoY  Start  (UT)      End
August 10: 2021.222:20:15:00 2021.222:20:44:59
August 11: 2021.223:13:33:13 2021.223:16:44:59  * overlap with XMM
August 12: 2021.224:11:56:15 2021.224:22:16:47
August 13: 2021.225:10:09:45 2021.225:16:44:59  * overlap with XMM
August 14: 2021.226:08:23:15 2021.226:18:43:47
August 15: 2021.227:06:46:16 2021.227:16:44:59  * overlap with XMM
August 16: 2021.228:04:59:46 2021.228:15:20:18
August 17: 2021.229:03:13:16 2021.229:13:33:48  * overlap with XMM
August 18: 2021.230:01:26:46 2021.230:11:47:18
August 19: 2021.231:00:00:00 2021.231:10:10:20  * overlap with XMM
August 19: 2021.231:22:03:18 2021.232:08:23:50
August 20: 2021.232:20:16:48 2021.233:06:37:20

While you should try to get data while HST and/or XMM are observing, it is also important to get as complete coverage as possible during this time period. Any observations August 9 through August 20 UT are valuable.

II. BP Tau
Position: 4 19 15.83 +29 06 26.9  (J2000)
Magnitude: V~12.1

This is a bright, classical T Tauri star in the Taurus star formation region for you northern observers. The rotation period is about 8 days. This is not as active an accretor as RU Lup; the TESS observations 2 years ago showed quasi-sinusoidal modulation with a 0.4 mag amplitude and a period of about 4.4 days.
Please try to get 1% BVRI photometry (0.01 mag precision), we we can determine colors to 2% or better.

The current HST schedule is:
Date                      DoY  Start  (UT)      End
August 20:    2021.232:19:20:28 2021.232:22:14:15
August 22:    2021.234:15:30:00 2021.235:00:00:00
August 24:    2021.236:15:15:00 2021.237:04:59:59
August 26:    2021.238:15:00:00 2021.239:04:59:59
August 28:    2021.240:16:05:42 2021.241:02:29:59
August 31:    2021.243:09:30:00 2021.243:09:59:58
September 01: 2021.244:18:31:12 2021.245:13:36:31
September 03: 2021.246:19:53:28 2021.246:23:59:59
September 05: 2021.248:21:06:13 2021.249:00:00:00
September 07: 2021.250:22:18:58 2021.251:04:29:59
September 09: 2021.252:23:31:43 2021.253:04:29:59
September 12: 2021.255:00:44:28 2021.255:04:29:59

While you should try to get data while HST is observing, it is also important to get as complete coverage as possible during this time period. Any observations August 19 through September 12 UT are valuable.

Note that all scheduled HST times are subject to change.