1. Semi-Regular Variable Star Population and Evolution Studies Jeff Wilkerson David Pfotenhauer Iowa Academy of Science April 18, 2015

2. OUR DATA SETS Cluster Dur. (s) # Nights Total ImagesDate Range NGC 6531 (M21)3.52130,00026 June 2002 – 8 Sept 2002 NGC 6514 (M23)3.52545,00019 June 2003 – 8 Sep. 2003 NGC 12910.5915,00011 Aug. 2003 – 8 Sep. 2003 NGC 2682 (M67)2.01435,00025 Feb. 2004 – 26 April 2004 NGC 6694 (M26)9.02028,00024 June 2004 – 9 Sep. 2004 NGC 6514 (M23)2.52045,00023 June 2005 – 30 Aug. 2005 NGC 22867.52228,00024 Jan. 2006 – 10 April 2006 NGC 6514 (M23)5.03749,00028 Mar. 2006 – 25 Sep. 2006 NGC 738010.04044,00012 Jul. 2006 – 9 Jan. 2007 NGC 22867.52944,00031 Oct. 2006 – 5 Apr. 2007 NGC 6514 (M23)2.84991,0009 Mar. 2007 – 27 Sep. 2007 NGC 738010.04248,0005 Jul. 2007 – 14 Jan. 2008 NGC 22865.03565,0003 Oct. 2007 – 12 Apr. 2008 NGC 6514 (M23)3.55382,0003 Mar. 2008 – 16 Sep. 2008 NGC 6514 (M23)3.54550,00011 Mar. 2009 – 17 Sep. 2009 NGC 6514 (M23)3.56359,00027 Feb. 2010 – 8 Oct. 2010 NGC 6514 (M23)3.55746,0001 Mar. 2011 – 11 Oct. 2011 NGC 6514 (M23)7.05341,00011 Feb. 2012 – 3 Oct. 2011 NGC 6514 (M23)7.04131,0001 Mar. 2013 – 1 Oct. 2013 NGC 6514 (M23)7.04028,00018 Feb. 2014 – 27 Sep. 2014 NGC 6514 (M23)7.0??1 Mar. 2015 – present

3. Student Participation: Ujjwal Joshi Nathan Rengstorf Andrea Schiefelbein Todd Brown Brajesh Lacoul Kari Frank Alex Nugent Drew Doescher Alex Sperry Jennifer Schulz Clara Olson Daniel Herman Joe Novak Robyn Siedschlag Siri Thompson Matt Fitzgerald Heather Lehmann Amalia Anderson Hilary Teslow Steve Dignan Kirsten Strandjord Donald Lee-Brown Andrew Becklin Ben Anderson David Pfotenhauer Zebadiah Howes Buena Vista Univ. Travis DeJong Dordt College Forrest Bishop Decorah High School Support: Roy J. Carver Charitable Trust (Grant #00-50) Luther College R.J. McElroy Trust/Iowa College Foundation American Astronomical Society Luther College HHMI

4. stars with F-Stat > 4.70 are variable +20 stars → We claim stars with F-Stat > 4.70 are intrinsically variable High cutoff chosen so ~0 Removed 7 stars with artificially high F-Stats: - 6 due to close neighbor interference - 1 due to transiting asteroid 55 remaining stars with F-Stat>4.70 Long Timescales: a variance test

6. http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/lowmass.html

7. 3/29 stars with periods.8 10/20 stars with periods > 270 days, amplitudes >.8 Populations Population Heterogeneity RV Tau 1654 2510 Evidence of at least two major subpopulations

9. Secular Trends Mean Magnitudes Gaussian Fit of the Slope Values shows: μ = 0.0086 ± 0.0019 mag/year Additionally 34 of the 44 show positive slopes μ 3_3 = 0.0053 ± 0.0020 mag/year μ ann = 0.0051 ± 0.0017 mag/year μ all = 0.0059 ± 0.0017 mag/year

10. http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/lowmass.html

11. http://zebu.uoregon.edu/~imamura/122/lecture-8/LMS.html

12. Mattei, J. A. and Foster, G., 2000, Trend Analysis of Long Period Variables, in Variable Stars as essential Astrophysical Tools, C. Ibanaglou (ed.), 485-502.

13. Secular Trends Data Normalization Normalization 1.Identify four reference images from throughout the night 2.Calculate average signal for each star in all four frames – this is the reference signal 3.Determine the signal of each star in the frame to be normalized – this is the sample signal 4.Calculate (ref. signal/sample signal) for each star 5.Normalization factor = median of all ratios in (4) 6.Inter-night normalization factor = median of all star signals: ref. night/data night All Images Unfiltered! The 126 brightest (of 252) “non-variable red stars” (R-I > 2.20) show slope μ = -0.0000023 ± 0.0000030 mag/year

15. http://zebu.uoregon.edu/~imamura/122/lecture-8/LMS.html

16. CONCLUSION We have a unique data set that offers unprecedented temporal coverage of >1600 stars down to 19 th magnitude, yielding a detection of variability in about 8% of the field stars. Strong evidence of two classes of pulsating stars (high/low amplitude, monoperiodic/multiperiodic) with different pulsation behavior. Observed secular evolution is most consistent with these stars largely or exclusively getting dimmer despite being on the AGB. Must remain aware of long tertiary periods. Must get a better handle on image normalization effects. Fuller assessment of the “non-variable” red stars in the field.