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 ID: 684700
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Slide1
Waiting and watching: Results from seven years of observing the field of open star cluster M23
Jeff WilkersonLuther CollegeRACJuly 13, 2010Slide2
We image 3 clusters per year: M23 and two others
Image durations: 2 to 12 seconds, unfilteredCampaign durations: 5 to 7 monthsReturn to a cluster at least onceBVRI photometry at least once for color correction to magnitude conversion and knowledge of variable star colorsResult: tens of thousands of images per cluster per yearHow did we get here? What are our goals?
Equipment: 12” Meade Schmidt-
Cassegrain
; Apogee AP6E
camera; SBIG STL-1001E camera
What We DoSlide3
Our Observational Goals:I. Brief changes in apparent stellar flux
Occultation and microlensing events Flare starsII. Very long timescale changes in stellar luminosity Luminosity stability Solar-like cycles6 Low-amplitude, ultra-long period pulsationIII. 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 planets5 Rotating variable star periods in young clusters7
Wyithe, J.S.B, and Wilson, R.E. 2002, ApJ, 571, 293
Rucinski, S.M. 1998, AJ, 116, 2998
Paczynski, B., et al. 2006, MNRAS, 368, 1311
Mochejska, B.J., et al. 2004, AJ, 128, 312
Mochejska, B.J., and Stanek, K.Z. 2006, AJ, 131,1090
Lockwood G.W., et al. 1997 ApJ, 485, 780-811
Herbst W. and Mundt R., 2005, ApJ, 633, 967-985Slide4
SkyandTelescope.com - News Blog - A KBO in the Crosshairs
Posted By Kelly Beatty, June 29, 2010Slide5
All images acquired with a 12” Meade LX200 and Apogee AP6E
camera or SBIG STL-1001E cameraSlide6
Student Participation:
Ujjwal JoshiNathan RengstorfAndrea SchiefelbeinTodd Brown Brajesh LacoulKari FrankAlex NugentDrew DoescherAlex Sperry
Robyn
Siedschlag
Siri
Thompson
Matt Fitzgerald
Heather Lehmann
Amalia
Anderson
Hilary TeslowSteve DignanKirsten StrandjordDonald 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 Slide7
OUR M23 DATA SETS
Duration (s)# Nights
Total Images
Date Range
3.5
25
45,000
19 June 2003 – 8 Sep. 2003
2.5
20
45,000
23 June 2005 – 30 Aug. 2005
5.0
37
49,000
28 Mar. 2006 – 25 Sep. 2006
2.8
49
91,000
9 Mar. 2007 – 27 Sep. 2007
3.5
53
82,000
3 Mar. 2008 – 16 Sep. 2008
3.5
45
50,000
11 Mar. 2009 – 17 Sep. 2009
3.5
~30
~32,000
24 Feb. 2010 – presentSlide8
From http://rst.gsfc.nasa.gov/Sect20/sun_mw+.jpgSlide9
DATA PROCESSING
All Analysis done with code developed in IDLCALIBRATIONDark Noise CorrectionFlat FieldingALIGNMENT Use a single frame for entire data set
STAR ID & EXTRACTION
Aperture photometry for signal determination
256 Background regions
INTRA-NIGHT NORMALIZATION
INTER-NIGHT NORMALIZATION
MAGNITUDE CONVERSIONSlide10
Frame Normalization
Identify four reference images from throughout the nightCalculate average flux for each star in all four frames – this is the reference signalDetermine the signal of each star in the frame to be normalized – this is the sample signalCalculate (ref. signal/sample signal) for each starNormalization factor = median of all ratios in (4)Slide11Slide12Slide13
Types of Variable Stars Pulsating (e.g., Mira, b Cephei,
d Cephei, d Scuti, RR Lyrae, a Cygni) Eclipsing (e.g., W UMa, Algol–type, b Lyrae) Cataclysmic RotatingSlide14
From Contemporary Activities in Astronomy, 2nd ed.
by Hoff and Wilkerson, Kendall-Hunt, 2003Slide15
We have identified 7 eclipsing binary systems in the field; they have periods ranging from 5 hours to several days.Slide16
From Variable Stars by M. Petit, Wiley and Sons, 1987
We see mostly SR and Mira starsIn the GCVS SR and Mira stars are about equally commonMiras have been better studied than SRs but still not well understoodSlide17
From
Mattei & Foster and Aslan & Yeśilyaprak in Variable Stars as Essential Astrophysical Tools (2000)Slide18Slide19Slide20Slide21
Is this a variable star?Slide22
We search for correlation in the signal using a modified f-test.Define :f = variance of full data set/variance of consecutive night differences81 times we have data on a night when we had data the previous nightRestrict 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-
m)/sSlide23Slide24
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 Slide25
Many more semi-regular than Mira stars; perhaps a break in the distribution.Slide26
The LPV stars are red, as expected.Slide27Slide28
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.