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Photometric Monitoring of the Field of Open Star Cluster M23 Jeff Wilkerson Iowa Academy of Science April 21, 2012 Sensitive to Variability on a Wide Range of Timescales: I. Tenths of seconds to seconds Occultation and microlensing events Brief flares II. Tenths of hours to a few days Flares in long period variables Delta Scuti stars Traditional flare stars Eclipsing binaries Transiting planets III. Days to hundreds of days Long period pulsating variable stars Eclipsing binary stars Cataclysmic variable stars Cepheid variables Period-to-period variability in long period variables Rotating variable stars in young clusters IV. Years to decades Luminosity stability Solar-like cycles Period-to-period variability in long period variables Proper motions of stars Have observed 61“classical” variable stars to date, 59 of them newly discovered Student Participation: Ujjwal Joshi Nathan Rengstorf Andrea Schiefelbein Todd Brown Brajesh Lacoul Kari Frank Alex Nugent Drew Doescher Alex Sperry Jennifer Schulz Clara Olson Robyn Siedschlag Siri Thompson Matt Fitzgerald Heather Lehmann Amalia Anderson Hilary Teslow Steve Dignan Kirsten Strandjord Donald Lee-Brown Andrew Becklin 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 OUR DATA SETS Cluster Dur. (s) # Nights Total Images Date Range NGC 6531 (M21) 3.5 21 30,000 26 June 2002 – 8 Sept 2002 NGC 6514 (M23) 3.5 25 45,000 19 June 2003 – 8 Sep. 2003 NGC 129 10.5 9 15,000 11 Aug. 2003 – 8 Sep. 2003 NGC 2682 (M67) 2.0 14 35,000 25 Feb. 2004 – 26 April 2004 NGC 6694 (M26) 9.0 20 28,000 24 June 2004 – 9 Sep. 2004 NGC 6514 (M23) 2.5 20 45,000 23 June 2005 – 30 Aug. 2005 NGC 2286 7.5 22 28,000 24 Jan. 2006 – 10 April 2006 NGC 6514 (M23) 5.0 37 49,000 28 Mar. 2006 – 25 Sep. 2006 NGC 7380 10.0 40 44,000 12 Jul. 2006 – 9 Jan. 2007 NGC 2286 7.5 29 44,000 31 Oct. 2006 – 5 Apr. 2007 NGC 6514 (M23) 2.8 49 91,000 9 Mar. 2007 – 27 Sep. 2007 NGC 7380 10.0 42 48,000 5 Jul. 2007 – 14 Jan. 2008 NGC 2286 5.0 35 65,000 3 Oct. 2007 – 12 Apr. 2008 NGC 6514 (M23) 3.5 53 82,000 3 Mar. 2008 – 16 Sep. 2008 NGC 6514 (M23) 3.5 45 50,000 11 Mar. 2009 – 17 Sep. 2009 NGC 6514 (M23) 3.5 63 59,000 27 Feb. 2010 – 8 Oct. 2010 NGC 6514 (M23) 3.5 57 46,000 1 Mar. 2011 – 11 Oct. 2011 NGC 6514 (M23) 7.0 ? ? 11 Feb. 2012 – present Short (II) Timescales: (tenths of hours to a few days) Primarily two types of objects here: Star 723 Summer 2010 Lightcurve Star 924 Lightcurve May24, 2010 14 12.8 (a) Flare stars 12.9 14.1 13 magnitude magnitude 14.2 13.1 13.2 14.3 13.3 14.4 13.4 14.5 2450 13.5 0 50 100 150 200 250 2500 2550 2600 300 CJD-2452800 Time (minutes) (a) Eclipsing binaries From Contemporary Activities in Astronomy, by Hoff and Wilkerson 2650 2700 How do we find these? WSVI-statistic test NGC 129 August 26, 2003 1.08 1. Fit a second-order polynomial to signalas a function of normalization factor 1.06 1.04 1.02 2. Define the WSVI* statistic to measure the deviation of a star’s signal from the polynomial fit using paired observations 1 0.98 0.96 0.94 0.92 3. Find the mean WSVI for a subset of stars 4. Measure each star’s WSVI deviation from the mean of its subset 0 20 40 60 80 Image Number 100 120 140 NGC 129 Star 35 8/26/03 125000 120000 115000 * Based on a variability index developed by Welch and Stetson (AJ, 105, 1993) 110000 105000 100000 95000 0.92 0.94 0.96 0.98 1 1.02 Normalization Factor 1.04 1.06 1.08 Eclipsing Binaries Period = 0.32866 days Star 16 Period = 0.5455059(2) days Period = 0.20730 days Star 41 Light Curve June 27, 2011 Star 1267 Lightcurve June 1, 2006 July 5, 2007 15.3 10.45 10.15 15.4 10.5 10.2 15.5 10.3 magnitude magnitude magnitude 15.6 10.25 15.7 15.8 10.55 10.6 15.9 10.65 10.35 16 16.1 10.4 0 0.5 1 1.5 2 2.5 3 Time After Start (Hrs) Period = 5.5 days 3.5 4 10.7 0 50 100 150 200 250 300 Time (minutes) Period = 1.883360(2) days 0 50 100 150 200 250 300 Time (min.) Period = 9.48665 days Eclipsing Binaries: April 17, 2012 <T2-T1>odd = 0.710±.053 hr <T2-T1>even = 0.782±.045 hr Star 1267 P =.94168030 d 0.02 <T3-T2>odd = 0.683±.042 hr O-C Even O-C Odd 0.015 <T3-T2>even = 0.703±.068 hr O-C (days) 0.01 <T4-T3>odd = 0.865±.041 hr 0.005 <T4-T3>even = 0.785±.075 hr 0 -0.005 -0.01 3s limit on LoS eccentricity ≈ 0.007 -0.015 -0.02 0 500 1000 1500 2000 2500 Cycle P = 1.883360(2)d (unc. ≈ 0.2 sec.) mO-C, even = 0.00024±.0009d mO-C, odd = -0.00025±.0009d In general: 3s limit on any variations ≈ 0.012d 3s limit on projection of eccentricity ≈ 0.001 (dP/dt)/P = 2(dm/dt)/(m1+m2) + 3(dm1/dt)(m1-m2)/m1m2 + 3K For us, 3s limit on dP/dt comes from 3s limit on O-C in 2011 vs. 2005 of 0.012d Pavg – Pobs = 5.2x10-6d DP = 1.04x10-5d in 2200 days (dP/dt)max = 4.5x10-9 Use sizes from eclipse timing and color to estimate m1 = 0.7Mʘ and m2 = 0.3Mʘ. dm1/dt < [(0.7Mʘ)(0.3Mʘ)/3Mʘ](4.5x10-9)/1.88d = 6x10-8 Mʘ/year sodd = 71.3 ADU seven = 206.6 ADU If the standard deviations are distributed normally then the variance of the of the standard deviation is: Var(s) = 1/N[N-1-2G2(N/2)/G2((N-1)/2)]Ns2/(N-1) Yields one standard deviation uncertainties: )4 (Ta/Tb = Depth1/Depth2 sodd = 71.3 +/-12.9ADU seven = 206.6+/-33.3 ADU One last check for a third star <T2-T1> = 0.746±.035 hr <T4-T3> = 0.825±.042 hr <T4-T2> = 1.494±.038 hr About 40% of the light goes away in either primary or secondary eclipse <T3-T1> = 1.437±.037 hr Total Light = C’(d12 +d22) = C[(.786)2 + (1.466)2] = C(.618 + 2.149) = C2.77 Fraction of total area from smaller object= 0.618/2.77 = 0.22 What if the secondary object is dark? Eclipse timing actually gives minimum large object radius due to orbital inclination. B-V = 1.415; V = 15.55 Assume reddening of cluster, = .356; (B-V)0= 1.059 Rstar≈0.80Rʘ Now need (Rdark/Rstar)2=0.40 Rdark ≈0.80Rstar ≈0.50Rʘ But we know brown dwarf stars have R ≈0.10Rʘ Assuming Rstar actually 2s below mean measured value and Rdark 2s above mean measured value yields fractional areal coverage of 0.355. If actual eclipse depth is 2s below mean measured value it would be 0.381. Star 166 Avg Depth vs. time 8 Avg O-C vs. time 0.004 7.5 0.002 Mean O-C (days) Avg. Annual Depth (%) 7 6.5 6 5.5 0 -0.002 5 4.5 4 May/1 -0.004 May/1 May/1 May/1 May/1 May/1 May/1 May/1 May/1 May/1 May/1 May/1 Date May/1 May/1 May/1 Date Mean O-C Primary and Seconday Eclipses Minima Depth Histogram Star 166 10 0.01 Even Numbered Minima Depth: mean = 6.47+/-0.24 % Mean O-C Odd Mean O-C Even Odd Numbered Minima: mean = 5.84+/-0.18 % 8 Odd depth Even depth 6 4 Mean O-C (days) # eclipses 0.005 0 -0.005 2 0 0.02 0.04 0.06 0.08 Depth (%) 0.1 0.12 -0.01 Apr/1 Apr/1 Apr/1 Apr/1 Apr/1 Date Apr/1 Apr/1 Apr/1 Long (IV) Timescales: a variance test s 2 s F-Stat Distribution 2 300 longterm 250 con sec utive nights We claim stars with F-Stat > 4.70 are intrinsically variable Number of Stars 200 stars with F-Stat > 4.70 are variable 150 100 High cutoff chosen so <FAP> ~0 +20 stars → 50 Removed 7 stars with artificially high F-Stats: 0 -5 0 5 F-Stat 10 15 - 6 due to close neighbor interference - 1 due to transiting asteroid 55 remaining stars with F-Stat>4.70 Pulsating Variables in the M23 Field Star 1654 15 magnitude 16 17 18 19 20 0 500 1000 1500 2000 2500 3000 MJD-2452800 Properties: Star 1654 15 16 magnitude Period: DCDFT Color: R-I Amplitude: 4-96% Asymmetry: Risetime/Period Mean Magnitude: (96+4)/2 17 18 2003 2005 2006 2007 2008 2009 2010 2011 19 20 0 0.2 0.4 0.6 MJD/154.29 - X 0.8 1 Populations of Pulsating Stars Star 356 Phase Diagram; = 96.3 Power Spectrum Lead Term Amplitude Histogram 8 13 7 13.5 6 1 14 magnitude # stars 5 4 14.5 15 3 15.5 2 16 1 16.5 0 0 20 40 60 80 0 100 0.2 Star 82 Phase Diagram; = 24.2 0.6 0.8 1 Star 981 Phase Diagram; = 42.3 1 11 0.4 MJD/321.42 - X DCDFT Theta One 1 14.5 14.6 11.2 14.7 magnitude magnitude 11.4 11.6 14.8 14.9 15 11.8 15.1 12 15.2 12.2 15.3 0 0.2 0.4 0.6 MJD/118.03-X 0.8 1 0 0.2 0.4 0.6 MJD/193.32 - X 0.8 1 Populations of Pulsating Stars Amplitude Distribution (F-Stat > 4.70) 20 y = 54.608 * x^(1.6583) R= 0.70793 We see many more lower A stars than higher A stars. 15 Recognize that detection efficiency is lower for lower A stars as well. 10 F-Stat Number of Stars 13.85<m<14.85 100 10 5 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 Amplitude (Magnitude) Estimated Fraction Variable per Mag of Amp Estimated Fraction of Stars Variable per Magnitude of Amplitude 0.4 Estimate the percentage of stars with A>0.22 mag. and P>10 days as : 3.6±0.6%. With cluster members removed the number is: 7.2±1.2%. 0.3 0.2 0.1 1 0.1 1 Amplitude (mag) Detection Efficiencies Deteff m<13.85 Deteff 13.85<m<14.85 Deteff 14.85<m<15.50 Deteff m>15.50 1 0.8 Efficiency 0 Fit a power law; extrapolate to threshold; use scatter to determine detection efficiency as a function of both magnitude and amplitude. 0.6 0.4 0.2 0 0 0 0 0.5 1 1.5 2 Amplitude of Variation 2.5 3 0.1 0.2 0.3 0.4 0.5 0.6 Amplitude of Variation (Magnitude) 0.7 0.8 Populations of Pulsating Stars PS Lead Term Amplitude Vs. Varaibility Amplitude Amplitude vs. Color 100 3 DCDFT Theta One 2.5 Amplitude 2 1.5 1 0.5 y = 70.573 * x^(0.24606) R= 0.4897 y = 84.718 * x^(0.99436) R= 0.52016 10 0 0.1 1 0 1 2 3 Amplitude (mag) Amplitude Vs. Period 5 6 7 Amplitude Vs. Best Period 3 3 2.5 2.5 2 2 Amplitude Amplitude 4 R-I 1.5 1.5 1 1 0.5 0.5 0 0 0 100 200 300 Period (days) 400 500 0 100 200 300 Period (days) 400 500 Interesting Stars: The Yellow Stars Star 338 Phase Diagram 12.5 13 A likely RV Tau variable magnitude 13.5 14 14.5 15 15.5 16 0 0.2 0.4 0.6 0.8 1 MJD-2452800/77.9 Star 357 Phase Diagram 13.3 13.4 magnitude 13.5 13.6 A likely Cepheid variable 13.7 13.8 13.9 14 0 0.2 0.4 0.6 MJD/14.898-X 0.8 1 Interesting Stars: Plateau Stars Star 317 Phase Diagram 12.5 Star 1223 Phase Diagram 13 13.5 13 magnitude magnitude 14 13.5 14 14.5 15 14.5 15.5 15 16 0 0.2 0.4 0.6 0.8 1 0 0.2 Star 1495 Phase Diagram 13.5 15 14 16 14.5 17 magnitude magnitude 0.4 0.6 0.8 1 MJD/389.61 - X MJD/367.64 - X 15 Star 1654 Lightcurve 18 19 15.5 20 16 0 0.2 0.4 0.6 MJD/394.73 - X 0.8 1 2500 2600 2700 2800 MJD-2452800 2900 3000 Interesting Stars: SAS Stars Star 1007 Lightcurve 14.6 14.8 15 magnitude 15.2 15.4 15.6 15.8 16 16.2 0 500 1000 1500 2000 2500 3000 2500 3000 MJD-2452800 Star 82 Lightcurve 11 11.2 magnitude 11.4 11.6 11.8 12 12.2 0 500 1000 1500 2000 MJD-2452800 Define Short-term Photometric Resolution (STPR) as s/m for a Gaussian fit to a histogram of several hundred signal measurements for a given star and Long-term Photometric Resolution (LTPR) as s/m for the nightly average signal measure of a given star over an entire campaign. LTPR vs Mean Stellar Signal (M23) M23 Data 1 0.1 0.1 0.01 0.01 100 1000 10 4 Stellar Signal (ADU) 10 5 100 1000 10 4 10 5 10 6 10 7 Mean Signal (ADU) At large signal values STPR approaches a constant (plateau) value determined by our frame normalization, itself limited by scintillation. For faint stars STPR increases as signal-1. In between STPR increases as signal-1/2. Counting statistics of the stellar signal measurement dominate STPR in this region. M23 Summer 2011 16 14 12 10 8 6 4 2 Functional fits shown of form: STPR=[(C1)² + (C2 signal-1/2)² + (C3 signal)2]1/2 0 0 0.05 0.1 Standard deviation of nightly signal over mean signal 0.15 M23 Color-Magnitude Color-Magnitude Diagram Diagram M23 Non-Variable Non-Variable HA Pulsating Pulsating Stars Stars HA LA Pulsating Pulsating Stars Stars LA Eclipsing Binaries Binaries Eclipsing 88 Star 16 10 10 Star 41 Star 69 II Star 166 12 12 Star 519 14 14 Star 1267 16 16 00 11 22 33 44 AVG R-I R-I AVG 55 66 77 Oddities CONCLUSION We have a unique data set that offers unprecedented temporal coverage of >1600 stars down to 19th magnitude, yielding a detection of variability in about 8% of the field stars. Have measured eclipsing binary periods down to tenths or hundredths of a second. Variation in orbital parameters gives information on perturbations in the system. Expect detections or stringent upper limits to appear in the next few years. Strong evidence of two classes of pulsating stars (high and low amplitude) with different pulsation behavior Distinct classes of pulsational behavior have emerged. Any model or models of these stars must account for the observed intra-group and inter-group homogeneity and heterogeneity. Brief, rare events in these stars and others are still being sought.