Alert Notice 750: T CrB photometry and spectroscopy requested for HST and XMM-Newton observations

August 3, 2021

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns and Observation Reports: https://www.aavso.org/t-crb-campaign-2021-2022
- Novae: https//www.aavso.org/t-crb-campaign-2021-2022-01
- Spectroscopy: https//www.aavso.org/t-crb-campaign-2021-2022-02

 
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!

Dr. Koji Mukai (NASA-GSFC, University of Maryland) and colleagues have requested AAVSO observers' assistance in monitoring the symbiotic recurrent nova T CrB in support of multiwavelength observations currently scheduled with HST (August 26) and XMM-Newton (to be determined) in August and September.

Dr. Mukai writes: "[Our] HST and XMM-Newton observations of the symbiotic recurrent nova, T CrB ... are part of our ongoing campaign to the current active state that started in 2016, and perhaps leading to its next nova eruption that might happen within the next 5 years or so.

"This campaign has long-term and short-term goals.

"Long-term: T CrB is a recurrent nova with known eruptions in 1866 and 1946. Although we can't depend on eruptions being strictly periodic, we anticipate the next eruption to happen soon - 2026 if the interval remains 80 years. Starting in late 2014, it has undergone an optical brightening event that reached its maximum in April 2016 and continues until today. We (Luna et al. 2020) argued that this is due to an increased accretion onto the white dwarf that is an essential part of how it accumulates enough hydrogen rich matter to fuel the next nova eruption.

"Our ultimate goal is to learn as much as possible about how T CrB and other novae accumulate the nuclear fuel needed for nova eruption.

"T CrB might suddenly drop down to its normal optical brightness. This did happen previously, ~1 year before the 1946 eruption. We don't know the cause of this. It may be that accretion rate drops to the normal level, or the active disk starts expelling a higher fraction of the matter (what we call "accretion disk wind") which then absorbs more of the light.

"But optical data alone aren't enough.  Blue light is an indicator of how much accretion is going on a certain distance away from the white dwarf.  UV data tell us about the accretion disk closer in, and X-ray data about accretion onto the white dwarf itself. Our coordinated XMM and HST observation (along with our monitoring campaign with Swift) is an effort to track the rate of accretion through the disk and onto the white dwarf, and the rate of wind mass loss, leading up to the next nova eruption in a few years' time.

"Short-term: We hope that the HST and XMM observations can be done within a few days of each other, but we can't expect them to be truly simultaneous. Optical monitoring can tell us if we need to account for changes in T CrB between the times of HST and XMM observations.

"Also, in the unlikely event that T CrB goes nova within the next month, we may have to cancel the observations, because it will then be too bright for HST!"

HST is currently scheduled to observe T CrB on 2021 August 26. The schedule for XMM is not yet known, but an observation within about a week of the HST observation was requested in the proposal that was accepted. The XMM schedule will be posted in the forum threads for this campaign when it is known.

Photometry and spectroscopy are requested beginning now and continuing for at least one week after the HST and XMM observations have occurred. For photometry, B is the main request and has highest priority. Dr. Mukai writes: "We would be particularly interested in B-band photometry, which we think is a reasonable proxy for accretion rate - certainly it is less affected by the variability of the red giant in this system than the data in redder filters...Data in other bands would be a bonus" (V, then Rc and Ic). DSLR observations are welcomed, as are visual observations.

Regarding cadence, Dr. Mukai writes: "During the second half of August, we'd like to see multiple points per calendar day - hopefully, with enough observers spread across the globe, we can get at least one point every 6 or 8 hours - that would be great." This does not mean each observer should observe multiple times per night; for any one observer, one observation per band per clear night is sufficient.

As with all HST observations, it will be crucial to have positive observations (V as well as B) of T CrB from the nights of August 24-25 and 25-26 to be able to give the HST team a positive magnitude 24 hours before the HST observation.

For spectroscopy, any resolution is acceptable. If flux calibration can be carried out, that would be preferred. For flux-calibrated spectroscopy, any of the stars in Hamuy's list would be fine, whichever is easier (http://www.ctio.noao.edu/noao/node/8963). The cadence should be the same as for photometry - one spectrum per observer per night. Regarding wavelength range, Dr. Mukai writes that "the H-alpha region is always useful, but we're also interested in the blue part of the spectrum."

Observers are asked to continue their photometric and spectroscopic coverage of T CrB at a lower cadence through the observing season and as soon as it becomes observable after solar conjunction, in preparation for additional HST and XMM observations planned for January/February 2022, as well as to monitor the system as it moves closer towards its next eruption.

Coordinates (2000.0): R.A. 15 59 30.16   Decl. +25 55 12.6 (from VSX page for T CrB)

Charts: Charts with comparison stars for T CrB may be created using the AAVSO Variable Star Plotter (VSP).

Submit observations: Please submit observations using the name T CRB to the AAVSO International Database or the AAVSO Spectroscopy Database as appropriate (see below for links).

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material provided by Koji Mukai.

----------------------------------

SUBMIT OBSERVATIONS TO THE AAVSO

Information on submitting observations to the AAVSO may be found at:
 - Photometry/visual observations: https://www.aavso.org/webobs
 - Spectroscopy: https://www.aavso.org/apps/avspec/

ALERT NOTICE ARCHIVE AND SUBSCRIPTION INFORMATION

An Alert Notice archive is available at the following URL:
https://www.aavso.org/aavso-alert-notices-for-observing-campaigns-and-discoveries

Subscribing and Unsubscribing may be done at the following URL:
https://www.aavso.org/aavso-alert-notice-subscribe

-------------------------------------------------

Please support the AAVSO and its mission -- Join or donate today:
https://www.aavso.org/apps/donate/