Irregularly Pulsating Red Giants Which to Observe, How, and Why

1. John R. Percy and Emil Terziev ----- Department of Astronomy & Astrophysics University of Toronto Toronto, Ontario, Canada Irregularly Pulsating Red GiantsWhich to Observe, How, and Why We acknowledge research support from the Natural Science and Engineering Council Of Canada, and the essential contribution of AAVSO observers and HQ staff.

2. Pulsating Red Giants • All red giants (and supergiants) are photometrically variable • The cooler the star, the larger the star, the longer the period, and the larger the amplitude • GCVS classification: Mira (M), semi-regular (SR), irregular (L) • Some stars are or may be multiperiodic; some have long secondary periods

3. General Considerations • AAVSO observers have amassed a gold mine of data, much of it not yet analyzed. There is science to be harvested. • Analysis and interpretation of these data make excellent projects for undergraduate students, and students in our high school Mentorship Program; they can develop and integrate science and research skills. • We publish the results in the JAAVSO, and present them at AAVSO meetings to inform, inspire, and thank the observers -- you

4. Why Observe Pulsating Red Giants? • Are they variable? Variability and amplitude as a function of temperature etc. • Classify them: are they periodic, semi-regular, or irregular? • Determine period(s): pulsation period(s), long secondary period, very long secondary periods? How do these depend on the properties of the star? • If irregular: determine form (“profile”) and nature of irregularity. Multiperiodic?

5. Irregular (L Type) Pulsating Red GiantsQuestions and our previous work • What is the nature and cause of the irregularity? Are they truly irregular, or is there a spectrum of behaviour from periodic, to semi-regular, to irregular? • Percy, Esteves, Lin, Menezes, & Wu, 2009, JAAVSO, 37, 71: “Quantifying 'Irregularity' in Pulsating Red Giants” • Percy & Long, 2010, JAAVSO, in press (ej121), “Further Studies of 'Irregularity' in Pulsating Red Giants” • Percy & Terziev, 2010, JAAVSO, in press, “Studies of 'Irregularity' in Pulsating Red Giants: Many More Stars, An Overview, and Some Conclusions”

6. Data and Analysis • Data: AAVSO visual observations from the International Database; 125 stars with 249 or more observations (out of a total of 900 L-type variables in the database) • Fourier Analysis: using Period04 from University of Vienna • Self-correlation Analysis: using our software developed by students at the University of Toronto; it is publicly available on-line. It provides a measure of the average observational error, the total variability, the periods or time scales, and a “profile” of the variability.

7. Results -- Spurious • Because of the seasonal gaps in the data, any real periods are accompanied by alias periods • Some stars show a spurious small-amplitude one-year period due to the Ceraski effect – a physiological effect which is a by-product of the process of visual observing • Some stars show a spurious small-amplitude one-month period, presumably due to the same effect • In the self-correlation diagram, a few stars show shallow minima at about 200 + 365N days, which we believe to be due to the Ceraski effect plus the effects of the seasonal gaps

8. ZZ Cam: Self-correlationspurious one-year period; non-variable

9. BO Car: Self-correlationthe 200 + 365N effect and profile

10. AA Cam: Fourier Analysisspurious one-year period; real 650-day period

11. V370 And: Fourier Analysis120-day period

12. V370 And: Self-correlation120-day period

13. Results -- Non-Spurious • A small fraction of the 125 stars showed clear periods of tens to hundreds of days, presumably due to pulsation • A small fraction of the stars showed small-amplitude long periods which may be the mysterious “long secondary periods” whose cause is unknown • About half of the stars appear to be irregular; no significant Fourier or self-correlation signals; we have determined variability “profiles” for them • Some appear to be not significantly variable, (but they may be microvariable) • Confirmation: there appears to be a spectrum of behaviour in L-type pulsating red giants, from fairly regular, through semi-regular, to irregular

14. Recommendations • Prime consideration: AAVSO observations should be scientifically useful • Periodic, amplitude 0.1 or more: observe visually, higher priority: 20 stars • Periodic, low-amplitude: observe visually, medium priority: 18 stars • Periodicity is uncertain, very low amplitude, or long period: observe visually (or not), lower priority: 14 stars • Irregular, drop from visual program: 55 stars • Not significantly variable: drop from visual program: 18 stars

16. Drop Some Stars from the Visual Program? • Most of our stars are not significantly variable, or irregular with known profile which will not change; science is known • Observe these photoelectrically;but thousands of small-amplitude red giants have already been discovered and studied in surveys • But they may “perform” in the future; not likely • Or show very long-term variability; that would take decades to establish [but a few could be followed up] • Stars with only a handful of (visual) observations have “a long way to go”; need years/decades of further observations • Bright variables can be studied by professional astronomers with other techniques e.g. interferometry; yes! • Existing observations would be “wasted”; yes, but so would any more observations; we have already extracted science from them

17. Thank You! ----- Surely this will provoke discussion!