Presentation on theme: "Waiting and watching: Results from seven years of observing the field of open star cluster M 23 Jeff Wilkerson Luther College RAC July 13, 2010."— Presentation transcript:
Waiting and watching: Results from seven years of observing the field of open star cluster M 23 Jeff Wilkerson Luther College RAC July 13, 2010
We image 3 clusters per year: M23 and two others Image durations: 2 to 12 seconds, unfiltered Campaign durations: 5 to 7 months Return to a cluster at least once BVRI photometry at least once for color correction to magnitude conversion and knowledge of variable star colors Result: tens of thousands of images per cluster per year How did we get here? What are our goals? Equipment: 12” Meade Schmidt-Cassegrain; Apogee AP6E camera; SBIG STL-1001E camera What We Do
Our Observational Goals: I. Brief changes in apparent stellar flux Occultation and microlensing events Flare stars II. Very long timescale changes in stellar luminosity Luminosity stability Solar-like cycles 6 Low-amplitude, ultra-long period pulsation III. Traditional Stellar Variability Surveys of new variable stars Locate detached and semi-detached eclipsing binaries in clusters 1 Locate contact eclipsing binaries in clusters 2 Period/amplitude variations in contact systems 3 Period-to-period variability in long period variables Search for cataclysmic variables in clusters 4 Search for transiting planets 5 Rotating variable star periods in young clusters 7 1.Wyithe, J.S.B, and Wilson, R.E. 2002, ApJ, 571, Rucinski, S.M. 1998, AJ, 116, Paczynski, B., et al. 2006, MNRAS, 368, Mochejska, B.J., et al. 2004, AJ, 128, Mochejska, B.J., and Stanek, K.Z. 2006, AJ, 131, Lockwood G.W., et al ApJ, 485, Herbst W. and Mundt R., 2005, ApJ, 633,
SkyandTelescope.com - News Blog - A KBO in the Crosshairs Posted By Kelly Beatty, June 29, 2010
All images acquired with a 12” Meade LX200 and Apogee AP6E camera or SBIG STL-1001E camera
Student Participation: Ujjwal Joshi Nathan Rengstorf Andrea Schiefelbein Todd Brown Brajesh Lacoul Kari Frank Alex Nugent Drew Doescher Alex Sperry Robyn Siedschlag Siri Thompson Matt Fitzgerald Heather Lehmann Amalia Anderson Hilary Teslow Steve Dignan Kirsten Strandjord Donald Lee-Brown 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
OUR M23 DATA SETS Duration (s)# NightsTotal ImagesDate Range ,00019 June 2003 – 8 Sep ,00023 June 2005 – 30 Aug ,00028 Mar – 25 Sep ,0009 Mar – 27 Sep ,0003 Mar – 16 Sep ,00011 Mar – 17 Sep ~30~32,00024 Feb – present
DATA PROCESSING All Analysis done with code developed in IDL 1.CALIBRATION Dark Noise Correction Flat Fielding 2.ALIGNMENT Use a single frame for entire data set 3.STAR ID & EXTRACTION Aperture photometry for signal determination 256 Background regions 4.INTRA-NIGHT NORMALIZATION 5.INTER-NIGHT NORMALIZATION 6.MAGNITUDE CONVERSION
Frame Normalization 1.Identify four reference images from throughout the night 2.Calculate average flux 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)
From Contemporary Activities in Astronomy, 2 nd ed. by Hoff and Wilkerson, Kendall-Hunt, 2003
We have identified 7 eclipsing binary systems in the field; they have periods ranging from 5 hours to several days.
From Variable Stars by M. Petit, Wiley and Sons, 1987 We see mostly SR and Mira stars In the GCVS SR and Mira stars are about equally common Miras have been better studied than SRs but still not well understood
From Mattei & Foster and Aslan & Yeśilyaprak in Variable Stars as Essential Astrophysical Tools (2000)
Is this a variable star?
We search for correlation in the signal using a modified f-test. Define : f = variance of full data set/variance of consecutive night differences 81 times we have data on a night when we had data the previous night Restrict our work to stars that appeared in our data at least 50% of the time 1566 stars. Compute f for stars in chunks of ~100 stars of similar brightness; define f-stat = (f- )/
169 stars have f-stat >2.0; 95 have f-stat >3.0; 58 have f-stat >4.0; 38 have f-stat > 5.0
Many more semi-regular than Mira stars; perhaps a break in the distribution.
The LPV stars are red, as expected.
CONCLUSION At least 50 to 100 (3 to 6%) of the stars in our field are classically variable. SR stars outnumber Miras by a large margin. The distribution of periods might be bi-modal. Stars with secular variations in measured signal appear to have gotten brighter more commonly than dimmer. Results are uncertain. Need better color measures and spectra. Need to monitor the field for several more years to understand secular variations and changes in our variable stars.