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Alert Notice 682: Observing campaign on Polars

October 16, 2019

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
 - Campaigns and Observing Reports
: https://www.aavso.org/observing-campaign-on-polars
 - Cataclysmic Variables: https://www.aavso.org/observing-campaign-on-polars-01

Drs. Kaya Mori (PI), Charles Hailey, Ninad Nirgudkar (Columbia University), and Gavin Ramsay (Armagh Observatory) are requesting AAVSO assistance in monitoring 5 polars in support of their X-ray study of these stars.

Dr. Mori writes: "Our team is running a long-term program of observing polars (i.e. highly-magnetized CVs) with NASA’s NuSTAR X-ray telescope. Since polars are highly variable (with ~50% duty cycle), we would like to schedule our X-ray observations when our targets are bright in the X-ray band...Using the future optical magnitude data obtained by AAVSO members [the optical and X-ray fluxes of magnetic CVs are positively correlated], we will make a decision on whether we should trigger X-ray observations or not.

"Our NuSTAR observations of polars in our neighborhood are the first crucial steps to resolve one of the long-standing problems in high-energy astrophysics - the source populations that comprise the Galactic Ridge X-ray emission. Nearly three decades ago, an X-ray haze that extends out from the Galactic Center for ~60 degrees in longitude and a few degrees in latitude was discovered and named as the Galactic ridge X-ray emission (GRXE). A series of very deep Chandra and XMM-Newton observations revealed that the GRXE consists of thousands of unresolved point sources largely dominated by magnetic cataclysmic variables (CVs); the exact X-ray populations of the GRXE are still unknown. Our NuSTAR observations [are part of our study of those populations]...

"We are requesting V (or CV if necessary) photometry two times per week. For CCD observations, it would be useful to have a 10-30 min sequence of data - this will help determine if there is any change in the brightness over the orbital period. [Cadence should be based on what is needed to attain a good S/N.] However, if this isn’t possible a single measurement is still very useful.

"When a target is found to be bright in the optical band, we will trigger the NuSTAR observations within 1-2 weeks. We will not need any further optical monitoring of that target once its NuSTAR observation is performed. Our NuSTAR observation program will run until the end of May 2020."

Targets:

Name RA (2000) Dec (2000) Range Type High State Threshold
UZ For 03 35 28.64 -25 44 21.8 17.0-20.9 V AM+E 18.0 V
VV Pup 08 15 06.79 -19 03 17.7 13.9-19.6 V AM+ELL 14.9 V
ST LMi 11 05 39.77 +25 06 28.6 14.4-18.5 V AM 15.4 V
V2301 Oph 18 00 35.53 +08 +08 10 13.9 14.7-22.0 V AM+E 15.7 V
EP Dra 19 07 06.16 +69 08 44.0 17.6-<21.0 V AM+E 18.5 V

Observers are requested to monitor these targets as indicated above, and to submit your observations to the AAVSO International Database in a timely manner. Scheduling of targets with NuSTAR and completion of needed coverage for targets will be posted in the AAVSO forum threads for this campaign (see URL above); please be sure to subscribe to the threads so you may stay up to date with the campaign.

AAVSO finder charts for these stars with comparison stars may be generated using the AAVSO Variable Star Plotter (VSP).

Please submit photometric observations to the AAVSO International Database using the names given in the table.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using information supplied by Dr. Mori.

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