AAVSO Alert Notice 746: High-resolution spectroscopy and photometry requested for rho Cas study

June 18, 2021

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns and Observation Reports: https://www.aavso.org/rho-cas-campaign
- Spectroscopy: https://www.aavso.org/rho-cas

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!

Ernst Pollmann (International Working Group ASPA (Active Spectroscopy in Astronomy, http://astrospectroscopy.de)) has requested AAVSO observers' assistance in obtaining high-resolution spectra of the very bright S Dor star rho Cas (HR 9045, 4.1-6.2 V) in support of a new long-term study. Photometry and visual observations are requested by the AAVSO.

Rho Cas is a yellow hypergiant that is demonstrating behavior that indicates it needs to be monitored closely. Pollmann writes: "Klochkova et al. (Astronomy Reports, vol. 62, no. 9 (2018)) report significant results of their analysis of long-term high-resolution spectroscopy, and they continue: 'In addition, photometric monitoring of the star (AAVSO) indicates that a new ejection of matter occurred in 2013, during which the brightness of the star decreased by 0.5m. This event occurred only 12 years after the previous one in 2000–2001 [brightness decreased by 1 mag]. Thus, the ejections in rho Cas are becoming more frequent. According to Lobel et al. (ApJ., 583, 923 (2003)) and Aret et al. (ASP Conf. Ser., 508, 357 (2017)), this may indicate that the star is approaching a crossing of the Yellow Void [of the H-R Diagram]. This fact suggests the urgent need of further monitoring of ρ Cas.'"
The figure below from Pollmann "shows Radial Velocity and Equivalent Width behavior of the last observed ejection from amateur observations (spectra of the BAA database) compared with the current state of Pollmann´s observation."


Observers are requested to obtain one spectrum per week with spectroscopic resolution of at least 10000 to 20000 (or higher).

Photometry (BVRI) and visual observations are requested by the AAVSO at the cadence of one observation per filter (or one visual observation) per week.

The campaign will continue until further notice (at least through 2024).

Observers contributing suitable spectra will be co-authors if the research results in a publication.

Coordinates (2000.0): R.A. 23 54 23.03  Dec. +57 29 57.8  (from VSX page for rho Cas)

AAVSO finder charts for rho Cas may be generated using the AAVSO Variable Star Plotter (VSP).

Spectra should be sent directly to Ernst Pollmann <ernst-pollmann@t-online.de> and also submitted to the AAVSO Spectroscopy Database (AVSpec), as well as to any other sites the observer chooses.

Photometry and visual observations should be submitted to the AAVSO International Database using the name RHO CAS.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material provided by Ernst Pollmann.

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/


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