Proposal #72

Co-investigators: John Martin (University of Illinois at Springfield) and Bill Rea (AAVSO, Christchurch, New Zealand)

The requested observations are part of an effort to determine Mira spectral types from low resolution spectra. Spectra will be obtained with the investigator's telescopes, though if grating spectra were available on the BSM they would be useful. We expect the requested observations could be carried out with BSM South and BSM Berry, possibly BSM Argentina could be suitable. The observations are to ensure that good coverage of the light curve is available to assist in determining the spectral types of the comparisons and that some colour variation data is available. The major draw backs to all the comparisons is that they are all variable to a greater or lesser extent. This is a common feature of giants with a spectral type of M.

Of the targets requested, R Oct, X Oct, and eps Oct are all listed in the BSM Epoch Photometry Database, though observations seem not to be available for some time.

Diffraction gratings such as the SA-100 and SA-200 are inexpensive and fit a standard filter wheel so that they can easily be incorporated into a variable star observing program such as is carried out by many amateurs. Further, many CCD cameras have sensitivity well into the infra-red where Miras put out most of their energy. Even though the spectra obtained are low resolution the large amplitudes and changes in spectrum structure together with their long periods means Miras can be usefully observed
with these types of spectroscopes. Having a reliable method of converting the spectral data to an estimated spectral would increase the value of observations made by amateur astronomers.

Major changes in the photosphere of Mira should detectable with these types of spectroscopes, in particular changes between oxygen and carbon rich atmospheres as a result of a dredge up event should be observable. Some Miras were termed ``Meandering Miras'' Uttenthaler (2011} and these Miras seem to have a C/O ratio very close to one. The authors suggest the meandering period may be due to small changes in the C/O ratio with on-going convection bringing up processed material from deep within
the interior. Shifts in the C/O ratio from less than one to greater than 1 result significant changes in the stellar atmosphere. Potentially these could be detected by long term
monitoring with low resolution spectrographs.

The main target is R Oct which is a Mira variable very close to the south celestial pole which makes it suitable for year round observing. It has been extensively observed visually with well over 8,000 observations in the AAVSO database. The period is listed as 407 days with spectral type range from M5.3 to M8.4. The variation of spectral type into the M7 and M8 classes means that we will need to switch from using the strength of the TiO lines to using VO lines, or using both, when trying to determine the spectral class in this part of its cycle. The Simbad database lists 74 papers which reference this star. While a lot of them appear to be the result of surveys and contain large numbers of other objects there are some which appear to have studied R Oct in some detail including some spectral studies. R Oct is in the Henry Draper catalogues (HD 40857) and the Hipparcos catalogue (HIP 25412). R Oct is listed as a target in the BSM catalogue and should currently be being observed in the V band. Adding the B filter would allow some colour variation data to be collected.

The six comparisons are now described.

CV Octans is classified as an LB variable, a slow irregular. It has been poorly observed by the AAVSO with no observations in its database. The source of the data appears to be the All Sky Automated Survey (ASAS) where it has the designation ASAS J165107-8708.2. The maximum variation observed is only about 0.23 magnitudes and a period of 56.89 days. VSX gives the spectral type as M3. The Simbad database lists six papers which reference this star. One is not in English the other five appear to all be the result of
surveys and contain large numbers of other objects. CV Oct is in the Henry Draper catalogues (HD 145548) and the Hipparcos catalogue (HIP 82459).

BQ Octans is classified as an LB variable, a slow irregular. It has been poorly observed with on 61 observations in the AAVSO database comprising mostly V band and only a few days from each of 2010, 2011, and 2012. The maximum variation observed is only about 0.35 magnitudes in the AAVSO data base but is given as 0.95 magnitudes in V
in the ASAS where it has the designation ASAS J143458-8946.2. Most of the time its variation is quite small with few observations deviating more than the 0.35 mag in the AAVSO database. The source of its M4 III spectral type is not given. The low amplitude of the variation may imply a relatively stable spectral type. The Simbad database lists 36 papers which reference this star. A number of these appear all be the result of surveys and contain large numbers of other objects. BQ Oct is in the Henry Draper catalogues (HD 110994) and the Hipparcos catalogue (HIP 71348).

X Octans is classified as an Mira variable. It has been reasonably well observed with 1159 observations in the AAVSO database beginning in 1987 comprising mostly visual observation with a small number of B, V, and R band observations. The maximum variation observed in V about 5.5 magnitudes. The high amplitude of the variation implies an unstable spectral type, which in the AAVSO database is given as M3e-M6e III. This is probably more accurate than the Simbad database which gives the variation as M5/M6e.
The Simbad database lists 21 papers which reference this star. All but one of them appear to be the result of surveys and contain large numbers of other objects. X Oct is in the Henry Draper catalogues (HD 91620) and the Hipparcos catalogue (HIP 51084). X Oct is currently listed as a BSM target in the V band. Adding the B filter would allow colour change data to be collected over its cycle.

eps Octans is classified as an SRB variable. It has observed between 1998 and 2012 with 627 observations in the AAVSO database comprising mostly V band with a small number of visual and B observations. The maximum variation observed is only about 0.78 magnitudes. The moderate amplitude of the variation may imply a relatively stable spectral type, however the spectral type is given as M5 III in both VSX and Simbad. The Simbad database lists 51 papers which reference this star. Many of them appear to be the result of surveys and contain large numbers of other objects. eps Oct is currently listed as a BSM target in the V band. Adding the B filter would allow colour change data to be collected over its cycle.

BW Octans is classified as an LB variable, a semi-regular late type giant. It has been poorly observed with on 81 observations in the AAVSO database comprising sporadic visual observations between 2013 and 2017. The maximum variation observed is about 1.8 magnitudes. However, ASAS gives its amplitude at 0.65 magnitudes in V. The spectral type is given as M5-M7 III in VSX and M7III in Simbad. The Simbad database lists 26 papers which reference this star. Many of them appear to be the result of
surveys and contain large numbers of other objects.

email address: rea.william@gmail.com