Alert Notice 734: HM Sge monitoring needed for HST and SOFIA observations

March 15, 2021

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Dr. Steven Goldman (Space Telescope Science Institute) and colleagues have requested AAVSO observers' assistance in monitoring the symbiotic Mira system HM Sge in support of observations scheduled with HST and SOFIA.

Dr. Goldman writes: "The purpose of this campaign is to support a joint SOFIA/HST Directors’ Discretionary program targeting HM Sge.  Observations will be obtained at wavelengths from the far-UV to the mid-IR.  The AAVSO...simultaneous data...will help constrain models of the system.  The observations will also alert us to any sudden activity that may pose a safety issue for the FUV detector.

"We are targeting a post-outburst (1975) symbiotic Mira system that displays a wide and diverse range of active astrophysical phenomena...With SOFIA we will probe the dust and the gas kinematics of the dense circumstellarbmaterial, and with HST we will map the gas in the inner nebula and probe the shocked emission. Collectively, our data will be used to study the detailed dynamics of the system and to characterize its long-term evolution as the system continues to relax decades after the explosion. The broad capabilities of these instruments allow us to study the overall impact of the outburst on the Mira’s circumstellar dust shell, the molecular flows, and the compact nebula surrounding the central engine.

"Observations are requested near the time of the HST and SOFIA observations to get a consistent snapshot of the spectral energy distribution, important for modeling the system. We are also interested in monitoring the system every night for the preceding week to look for any sudden changes in brightness."

Two HST instruments will be observing HM Sge. The COS observations have been scheduled for 2021 March 21 02:20:54 - 07:36:11 UT. The WFC3 observations are scheduled for sometime between now and April 7. SOFIA observations will also take place during this period. The final time for the WFC3 observations will be announced in the forum threads given above for this campaign.

Nightly visual observations are requested beginning now and continuing though 2021 April 14. Nightly CCD snapshots (Johnson filter priority V, B, U) are also requested. It is important to have coverage throughout the interval so as to know the status of the system. The most recent observation in the AAVSO International Database showed HM Sge at visual magnitude 12.3 on 2020 December 16.838 UT (G. Poyner, Birmingham, UK).

Dr. Goldman notes that observers making a significant contribution to the research through their data will be considered for co-authorship.

As a final note, Dr. Goldman adds: "We would like to thank the AAVSO for their previous observations of HM Sge, and highlight the importance of the continued long-term monitoring of the fascinating system."

Coordinates (2000.0): 19 41 57.07 +16 44 39.6  (from VSX page for HM Sge)

Finder charts with comparison stars may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the name HM SGE.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material provided by Dr. Goldman.



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