Alert Notice 738: R Aqr monitoring needed in support of Chandra and HST observations

Note:  The minimum of R Aqr has passed; ongoing observations, especially in B and V, are essential. Please continue to observe R Aqr until further notice.  -  Elizabeth O. Waagen, July 5, 2022

The HST observations were successfully obtained. Please continue to observe R Aqr until further notice.  -  Elizabeth O. Waagen, July 6, 2021

The Chandra observations have been completed. The HST observations will take place 2021 May 13 10:57:01 - 18:08:28 UT.  -  Elizabeth O. Waagen, May 4, 2021

April 5, 2021

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns and Observation Reports:
- Long Period Variables:
- Spectroscopy:

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. Margarita Karovska (Center for Astrophysics|Harvard & Smithsonian) requests the assistance of AAVSO observers in monitoring the symbiotic binary (Mira + white dwarf) R Aqr in support of upcoming observations with Chandra and HST.

The Chandra observations are scheduled for the week of 2021 April 26-May 2 UT. The HST observations are scheduled for the week of May 17-23 UT. When the exact dates/times of the observations are known, they will be posted in the forum threads given above for this campaign.

R Aqr is just emerging from its seasonal gap, and coverage is essential as soon as it is possible to pick it up in the dawn twilight. It is critical to have some nights of positive observations prior to the satellite observations.

Starting now, Dr. Karovska requests photometry, primarily V and B photometry, and then UIRH, and if at all possible mid-IR photometry. High-speed UB photometry and spectroscopy are also requested. Visual observations will be very valuable and are strongly encouraged.

The cadence requested is twice a week, then nightly during the scheduled Chandra and HST observations, then twice a week for two weeks after the satellite observations.

R Aqr is presently undergoing the eclipse that occurs about every 40 or so years. Dr. Karovska reports that "the effects of the periastron are still visible including dimming of the light curve, absorbing the emission from the Mira and perhaps the binary itself by material that has been recently ejected."

R Aqr has a V range of 5.2-12.4. It has been behind the Sun since 2021 February - the most recent observation from the AAVSO International Database showed it at visual magnitude 12.0 on 2021 February 01.0565 UT (B. Cudnik, Houston, TX).

Coordinates (J2000): R.A. 23 43 49.46  Dec. -15 17 04.2  (from VSX page for R Aqr)

Charts with comparison stars for R Aqr may be created using the AAVSO Variable Star Plotter (VSP).

Please report all photometry observations to the AAVSO International Database using the name R AQR. Spectroscopy reports should be submitted to the AAVSO Spectroscopy Database (AVSpec) and to Dr. Karovska (

This Alert Notice was compiled by Elizabeth O. Waagen.


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