Program stars

My main interest is on observations of stars of [very] high luminosity. These tend to be spectroscopically variable (which makes them more interesting for monitoring) and in some cases we may even witness stellar evolution on timescales of decades:

• long-time monitoring of post-AGB stars (RV Tauri, SRD variables) - currently (2021) suspended
• massive OB stars (P Cygni) and yellow hypergiants (HR8752) - currently (2021) suspended
• monitoring of H-alpha emission in S/C-type Miras and SRA [SRB] variables

In 2016/2017 I have begun to monitor H-alpha emission as function of photometrical phase. Because of the large light amplitudes, only the brightest Miras can be followed spectroscopically over the complete phase.

H-alpha emission seems to be observable only between phases ~0.8 to 0.3 (although higher spectral resolution might increase the observable timespan). Thus it is not necessary to follow the star through minimum light, which increases the number of observable Miras.

My useful observing limit lies with magnitude 9 -9.5 near H-alpha which translates for these red stars to V~10.5 to 11.0 .

Several M-type Miras were observed near maximum light, but without results (explanation).

Strong H-alpha emission was observed in C-type Miras. Best phase coverage is currently obtained for

• W Cas
• U Cyg
• R Gem (S-type)
• R Ori

Other C-type (and S[C]-type) Miras that I try to follow are:

• U Lyr
• RS Cyg
• WX Cyg
• chi Cyg  (S-type)
• R Cyg (S-type)
• T Lyn
• R CMi (SC-type)
• V Boo (MS-type)
• V Cnc (S-star)
• S Cam
• T Cam (S-type)
• S Cep
• V CrB
• X Cas
• RZ Peg
• SY Per
• V Oph (too far south for good phase coverage)
• V374 Aql (too far south for good phase coverage)

Also semi-regular giants of variability type (from GCVS) SRA [and possibly SRB] show H-alpha emission (if their amplitudes are large enough to generate pulsational shocks). Since these SRs show smaller amplitudes than the Miras, more of these may be observed over the complete light-curve. Best observed are ST And and WZ Cas (which is also interesting because of the very strong Lithium line at 670.8nm)

For bright northern Carbon- and S-star regular pulsators (Miras, SRAs [, SRBs]) I maintain a list with predictions of the pulsation phase, to see if they may be worthwhile to observe spectroscopically.

The phases are derived based on the GCVS pulsation periods and the last date of maximum (or maxima, if more than one).

Phases >1.0 denote that the maximum is from a previous pulsation cycle.

Most maxima are taken from (visual) lightcurves on the AAVSO website. For some weaker stars not observed by AAVSO I use occasionally surveys such as ASAS-SN.

See the lists here.