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RS Sge Observations & Preliminary Analyses

RS Sge Observations & Preliminary Analyses. Jerry Horne AAVSO Fall Meeting 30 October 2010. Outline. Abstract Background Previous Observations Current Observations Looking for Eclipses Conclusions. Abstract.

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RS Sge Observations & Preliminary Analyses

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  1. RS Sge Observations & Preliminary Analyses Jerry Horne AAVSO Fall Meeting 30 October 2010 AAVSO

  2. Outline • Abstract • Background • Previous Observations • Current Observations • Looking for Eclipses • Conclusions AAVSO

  3. Abstract New V, B, Ic, and R band photometry or RS Sge is obtained. These new observations, when combined with other published observational data, allowed the determination of multiple period values for each star. From its multi-period behavior and from an examination of other intrinsic parameters, RS Sge was confirmed to be that of an RVb Tauri type star, with an fundamental period of 79.4 days with a longer amplitude modulation of 1174 days. AAVSO

  4. Outline • Abstract • Background • Previous Observations • Current Observations • Looking for Eclipses • Conclusions AAVSO

  5. Introduction • RS Sge first appears as a variable in the German Publication Astronomiche Nachrichten in 1905. • It was also noted as a variable by Walter Baade in 1928, who provided more precise coordinates. • Apparently, the first detailed study of the star was published by V. Tsessevich in 1977. He reported both “fast” and “slow” fluctuations in the light curve over an approximately 20 year period. • Two Algol-like “fades” were reported by V.I Kardopolov and G.G. Filip’e in 1985 AAVSO

  6. Introduction • The RS Sge designation in the GCVS is RVB+EA. • An RV Tauri type b star (RVb) • It is the only RV Tauri star in the GCVS which is also indicated as an eclipsing binary (EA) • The variability is listed as: 11.7 - 15.9 p • The period is listed as: 82.395 days 710011 |RS Sge *|195706.4+195944 |RVB+EA | 11.7 | 15.9 |p | AAVSO

  7. Background • Interest in RS Sge appears in several AAVSO communications, most recently: • Eyepiece Views: • July 2007 - A DIFFERENT VIEW OF RV TAURI STARS “ It is definitely worthwhile to put this and other RV Tauri stars on your observing program.” - Eric Broens E Y E P I E C E V I E W S #321 ---------------------------------------- July, 2007 AAVSO

  8. Background N E R.A. 19 57 06.42 Dec. 19 59 43.7 (2000.0) AAVSO

  9. Background N E R.A. 19 57 06.42 Dec. 19 59 43.7 (2000.0) AAVSO

  10. Background • RV Tauri stars: • Are regular or semi-regular variables • Are luminous stars of F or G at maximum light and G or early K at minimum light. • Show complex light and spectral changes • Have Periods between 30 and 150 days AAVSO

  11. Background • Common RV Tauri characteristics: • Alternating deep and shallow minima in the light and color curves • Secondary minima depths are more variable that primary minima depths • A mean phase lag exists between the color index and light curves • The RVb subclass, exhibits a long term variability, beyond the alternating minima, with periods from hundreds to thousands of days. AAVSO

  12. Outline • Abstract • Introduction and Background • Previous Observations • Current Observations • Looking for Eclipses • Conclusions AAVSO

  13. RS Sge Previous Observations IBVS 1371 (1977). From observations by Tsessevich: AAVSO

  14. RS Sge Previous Observations Long Term variability of RS Sge. From observations by Tsessevich published in 1977 AAVSO

  15. RS Sge Previous Observations Long Term variability of RS Sge. From observations by Tsessevich published in 1977 AAVSO

  16. RS Sge Previous Observations • V.I. Kardopolov and G.K. Filip’e (1985) focused on the short term variability and reported: • Concerning the alternating minima of RV Tauri stars: • Max I: 11.1 mag Min I: 12.0 mag • Max II: 11.25 mag Min II: 11.70 mag • A fundamental period of approximately 90 days • Algol-like fades on JD 2444837.22 and 2444865.17 AAVSO

  17. RS Sge Previous Observations 11.0 12.0 ~90 d Short Term variability of RS Sge. From photoelectric observations by V.I. Kardopolov and G.K. Filip’e published in 1985 AAVSO

  18. RS Sge Previous Observations Long Term variability of RS Sge. From observations submitted to the AAVSO (Trend line added). AAVSO

  19. RS Sge Previous Observations Pojmanski, in 2008, published observations on RS Sge as part of the data from the All Sky Automated Survey (ASAS) for 2003-2008: AAVSO

  20. RS Sge Previous Observations Visual magnitude of RS Sge. From ASAS observations from 2003-2008 Eclipses? AAVSO

  21. ASAS RS Sge Data • Some issues with the ASAS data: • Possible eclipses are listed as > 14.5 mag. • Apparently this is a cutoff mag, not the eclipse depth. • The data contains some probable anomalies: • 2453625.582 14.5 • 2453625.584 12.84 • RS Sge apparently gained 1.66 mags in 3 minutes • Close pairs of eclipse data points (e.g.): • 2453125.851 14.5 • 2453128.867 14.5 • Have varying intervals of 2.9, 3.1, and 3.90 days • Period and Self-Correlation analysis could not determine a unique period from the eclipse data points. AAVSO

  22. ASAS RS Sge Data • Assuming at least some subset of the data actually represents an eclipse; • Part of the problem trying to analyze the ASAS “eclipse” data is the time given for the observation only represents: • A time during the eclipse when the magnitude was below 14.5. • It is not the midpoint of the eclipse • Each time listed includes a variance away from the eclipse mid-point. • Since we don’t know the length of the eclipse, this variance could be minutes to hours in size. AAVSO

  23. ASAS RS Sge Data Mid Point of Eclipse ASAS Cutoff Mag Typical Eclipse Light Curve +/- Timing Variance AAVSO

  24. Outline • Abstract • Introduction and Background • Previous Observations • Current Observations • Looking for Eclipses • Conclusions AAVSO

  25. Current RS Sge Observations • In Dec 2009, a project to observe RS Sge was begun with the AAVSOnet telescopes, chiefly, • W30 (Wright-30) a 30-cm Meade LX200 also located at the Astrokolkhoz telescope facility near Cloudcroft, New Mexico • SRO, a C14 telescope located at the Sonita Research Observatory in Arizona. • Images were captured in BVRI bands. • Additional observations were made with a 0.25m SCT in V band, once the monsoon season started in the U.S. Southwest. AAVSO

  26. RS Sge Observations Visual magnitude of RS Sge. From AAVSOnet observations in 2010 AAVSO

  27. RS Sge Observations Comparison of light curve for RS Sge. From AAVSOnet observations in 2010 (left) and photoelectric observations by V.I. Kardopolov and G.K. Filip’e published in 1985 (right). AAVSO

  28. RS Sge Observations Visual magnitude of RS Sge. From observations by the author in 2010 AAVSO

  29. RS Sge Observations Ic magnitude of RS Sge. From AAVSOnet observations in 2010 AAVSO

  30. RS Sge Observations V bandminima Expected Phase Lag V - I minima V color curve and V – I color Index of RS Sge. From AAVSOnet observations in 2010 AAVSO

  31. Outline • Abstract • Introduction and Background • Previous Observations • Current Observations • Looking for Eclipses • Conclusions AAVSO

  32. RS Sge Eclipses • One of the primary reasons for this study is to understand the EA portion of the classification – the eclipses. • We do have an upper bound on the period: • Kardopolov and Filip’e (1985) described two eclipses separated by 27.95 days • The period then has to be either < 14 (28/n) days • or ~28 days • Can the noted time variance of the ASAS data be used to help determine possible periods for the eclipse, and guide subsequent observations? AAVSO

  33. RS Sge Eclipses Iterate over various Eclipse Periods ASAS Cutoff Mag That minimizes the difference between the period and the ASAS data AAVSO

  34. RS Sge Eclipses • What needs to be done is: • Iterate over a large number of periods • Measure the difference between the calculated time of eclipse vs the actual data. • Sum the differences for all eclipse data points • Find the minimum variance for the various possible period intervals (1-2 days, 2-3, days…). • A little programming in Excel can do this. AAVSO

  35. RS Sge Eclipses • The resulting candidate periods: AAVSO

  36. RS Sge Eclipses • Observational data vs candidate periods: AAVSO

  37. RS Sge Eclipses • Other shorter periods virtually eliminated by a combination of AAVSOnet data and authors observations (~10k images) • Only remaining viable period appears to be ~28 days • If we use the Kardopolov and Filip’eperiod between observations of the eclipse: • 27.95 days • There was one eclipse visible in 2010 in U.S. time zones: • Feb 16, 0340 Z • For 2011: • Mar 14 1050 Z, Apr 11 0940Z, May 9 0828Z … • This would be somewhat consistent with the ASAS data AAVSO

  38. Outline • Abstract • Introduction and Background • Previous Observations • Current Observations • Looking for Eclipses • Conclusions AAVSO

  39. Conclusions • Current and recent observations of RS Sge: • Confirmed the RVb classification • ~80 day fundamental period • ~1200 day long term variation • No eclipses seen in 2010 • Period probably ~28 days • More observations needed • Especially starting in Mar 2011 AAVSO

  40. References • American Association of Variable Star Observers, 2010, http://www.aavso.org/; http://www.aavso.org/publications/eyepieceviews/0707.pdf • General Catalog of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. http://www.sai.msu.su/groups/cluster/gcvs/gcvs/ • Kardopolov, V. and Filip’e, G, 1986, SvA, 32, 424K • Pojmanski, G. 2002, Acta Astron. 52,397 • Pollard, K.R., P.I. Cottrell, W.A. Lawson, and A.C. Gilmore, 1996, Monthly Notices of the Royal Astronomical Society, 279, 949-977 • Tsessevich, V., 1977, IBVS 1371 • Skiff, B, 1997, IBVS 4459 AAVSO

  41. Questions? AAVSO

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