photometric monitoring of the field of open star cluster m23
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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 - PowerPoint PPT PresentationTRANSCRIPT
Photometric Monitoring of the Field Photometric Monitoring of the Field ofof
Open Star Cluster M23Open Star Cluster M23
Jeff WilkersonJeff WilkersonIowa Academy of Iowa Academy of
ScienceScience
April 21, 2012April 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 SchiefelbeinTodd BrownBrajesh 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 HowesBuena Vista Univ.
Travis DeJongDordt College
Forrest BishopDecorah High School
Support: Roy J. Carver Charitable Trust (Grant #00-50)Luther CollegeR.J. McElroy Trust/Iowa College FoundationAmerican 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:
(a)Flare stars
(a)Eclipsing binaries
From Contemporary Activities in Astronomy, by Hoff and Wilkerson
14
14.1
14.2
14.3
14.4
14.52450 2500 2550 2600 2650 2700
Star 723 Summer 2010 Lightcurve
ma
gn
itud
e
CJD-2452800
12.8
12.9
13
13.1
13.2
13.3
13.4
13.50 50 100 150 200 250 300
Star 924 Lightcurve May24, 2010
ma
gn
itud
e
Time (minutes)
How do we find these? WSVI-statistic test
1. Fit a second-order polynomial to signalas a function of normalization factor
2. Define the WSVI* statistic to measure the deviation of a star’s signal from the polynomial fit using paired observations
3. Find the mean WSVI for a subset of stars
4. Measure each star’s WSVI deviation from the mean of its subset
* Based on a variability index developed by Welch and Stetson (AJ, 105, 1993)
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
1.08
0 20 40 60 80 100 120 140
NGC 129 August 26, 2003
Image Number
95000
100000
105000
110000
115000
120000
125000
0.92 0.94 0.96 0.98 1 1.02 1.04 1.06 1.08
NGC 129 Star 35 8/26/03
Normalization Factor
Eclipsing Binaries
Period = 0.32866 days Period = 0.5455059(2) days Period = 0.20730 days
10.15
10.2
10.25
10.3
10.35
10.40 0.5 1 1.5 2 2.5 3 3.5 4
Star 16 July 5, 2007
ma
gn
itud
e
Time After Start (Hrs)
Period = 5.5 days Period = 1.883360(2) days
15.3
15.4
15.5
15.6
15.7
15.8
15.9
16
16.10 50 100 150 200 250 300
Star 1267 Lightcurve June 1, 2006
ma
gn
itu
de
Time (minutes)
10.45
10.5
10.55
10.6
10.65
10.70 50 100 150 200 250 300
Star 41 Light Curve June 27, 2011
ma
gn
itud
e
Time (min.)
Period = 9.48665 days
Eclipsing Binaries: April 17, 2012
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0 500 1000 1500 2000 2500
Star 1267 P =.94168030 d
O-C EvenO-C Odd
O-C
(d
ays)
CycleP = 1.883360(2)d O-C, even = 0.00024±.0009d (unc. ≈ 0.2 sec.) O-C, odd = -0.00025±.0009d
3 limit on any variations ≈ 0.012d 3 limit on projection of eccentricity ≈ 0.001
<T2-T1>odd = 0.710±.053 hr
<T2-T1>even = 0.782±.045 hr
<T3-T2>odd = 0.683±.042 hr
<T3-T2>even = 0.703±.068 hr
<T4-T3>odd = 0.865±.041 hr
<T4-T3>even = 0.785±.075 hr
3 limit on LoS eccentricity ≈ 0.007
In general:
(dP/dt)/P = 2(dm/dt)/(m1+m2) + 3(dm1/dt)(m1-m2)/m1m2 + 3K
For us, 3 limit on dP/dt comes from 3 limit on O-C in 2011 vs. 2005 of 0.012d
Pavg – Pobs = 5.2x10-6d P = 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
(Ta/Tb)4 = Depth1/Depth2
odd = 71.3 ADU
even = 206.6 ADU
If the standard deviations are distributed normally then the variance of the of the standard deviation is:
Var() = 1/N[N-1-22(N/2)/2((N-1)/2)]N2/(N-1)
Yields one standard deviation uncertainties:
odd = 71.3 +/-12.9ADU
even = 206.6+/-33.3 ADU
One last check for a third star
About 40% of the light goes away in either primary or secondary eclipse
<T2-T1> = 0.746±.035 hr
<T4-T3> = 0.825±.042 hr
<T4-T2> = 1.494±.038 hr
<T3-T1> = 1.437±.037 hr
Total Light = C’(d12 +d2
2) = 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
Eclipse timing actually gives minimum large object radius due to orbital inclination.
What if the secondary object is dark?
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 2 below mean measured value and Rdark 2 above mean measured value yields fractional areal coverage of 0.355.
If actual eclipse depth is 2 below mean measured value it would be 0.381.
4
4.5
5
5.5
6
6.5
7
7.5
8
May/1 May/1 May/1 May/1 May/1 May/1 May/1 May/1
Avg Depth vs. timeA
vg.
An
nu
al D
ep
th (
%)
Date
Star 166
-0.01
-0.005
0
0.005
0.01
Apr/1 Apr/1 Apr/1 Apr/1 Apr/1 Apr/1 Apr/1 Apr/1
Mean O-C Primary and Seconday Eclipses
Mean O-C OddMean O-C Even
Me
an
O-C
(d
ays
)
Date
-0.004
-0.002
0
0.002
0.004
May/1 May/1 May/1 May/1 May/1 May/1 May/1
Avg O-C vs. time
Me
an
O-C
(d
ays
)
Date
0
2
4
6
8
10
0.02 0.04 0.06 0.08 0.1 0.12
Minima Depth Histogram Star 166
Odd depthEven depth
# e
clip
ses
Depth (%)
Even Numbered Minima Depth:mean = 6.47+/-0.24 %
Odd Numbered Minima:mean = 5.84+/-0.18 %
0
50
100
150
200
250
300
-5 0 5 10 15
F-Stat Distribution
Num
ber
of S
tars
F-Stat
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 <FAP> ~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 (IV) Timescales: a variance test
2
2
sec
nightsutivecon
longterm
Pulsating Variables in the M23 Field
Properties:
Period: DCDFTColor: R-IAmplitude: 4-96%Asymmetry: Risetime/PeriodMean Magnitude: (96+4)/2
15
16
17
18
19
200 500 1000 1500 2000 2500 3000
Star 1654
ma
gn
itud
e
MJD-2452800
15
16
17
18
19
200 0.2 0.4 0.6 0.8 1
Star 1654
20032005200620072008200920102011
mag
nitu
de
MJD/154.29 - X
Populations of Pulsating Stars
11
11.2
11.4
11.6
11.8
12
12.20 0.2 0.4 0.6 0.8 1
Star 82 Phase Diagram; 1 = 24.2
ma
gn
itud
e
MJD/118.03-X
0
1
2
3
4
5
6
7
8
0 20 40 60 80 100
Power Spectrum Lead Term Amplitude Histogram
# s
tars
DCDFT Theta One
13
13.5
14
14.5
15
15.5
16
16.50 0.2 0.4 0.6 0.8 1
Star 356 Phase Diagram; 1 = 96.3
ma
gn
itud
e
MJD/321.42 - X
14.5
14.6
14.7
14.8
14.9
15
15.1
15.2
15.30 0.2 0.4 0.6 0.8 1
Star 981 Phase Diagram; 1 = 42.3
mag
nitu
de
MJD/193.32 - X
Populations of Pulsating StarsWe see many more lower A stars than higher A stars.
Recognize that detection efficiency is lower for lower A stars as well.
Fit a power law; extrapolate to threshold; use scatter to determine detection efficiency as a function of both magnitude and amplitude.
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
5
10
15
20
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
Amplitude Distribution (F-Stat > 4.70)
Num
be
r o
f S
tars
Amplitude (Magnitude)
0
0.2
0.4
0.6
0.8
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Detection Efficiencies
Deteff m<13.85Deteff 13.85<m<14.85
Deteff 14.85<m<15.50Deteff m>15.50
Eff
icie
ncy
Amplitude of Variation (Magnitude)
0
0.1
0.2
0.3
0.4
0 0.5 1 1.5 2 2.5 3
Estimated Fraction of Stars Variable per Magnitude of Amplitude
Est
imat
ed F
ract
ion
Var
iab
le p
er
Ma
g of
Am
p
Amplitude of Variation
1
10
100
0.1 1
13.85<m<14.85
y = 54.608 * x^(1.6583) R= 0.70793
F-S
tat
Amplitude (mag)
Populations of Pulsating Stars
10
100
0.1 1
PS Lead Term Amplitude Vs. Varaibility Amplitude
y = 70.573 * x^(0.24606) R= 0.4897
y = 84.718 * x^(0.99436) R= 0.52016
DC
DF
T T
he
ta O
ne
Amplitude (mag)
0
0.5
1
1.5
2
2.5
3
0 1 2 3 4 5 6 7
Amplitude vs. Color
Am
plit
ude
R-I
0
0.5
1
1.5
2
2.5
3
0 100 200 300 400 500
Amplitude Vs. Best Period
Am
plitu
de
Period (days)
0
0.5
1
1.5
2
2.5
3
0 100 200 300 400 500
Amplitude Vs. Period
Am
plitu
de
Period (days)
Interesting Stars: The Yellow Stars
A likely Cepheid variable
A likely RV Tau variable
12.5
13
13.5
14
14.5
15
15.5
160 0.2 0.4 0.6 0.8 1
Star 338 Phase Diagram
ma
gn
itud
e
MJD-2452800/77.9
13.3
13.4
13.5
13.6
13.7
13.8
13.9
140 0.2 0.4 0.6 0.8 1
Star 357 Phase Diagram
ma
gn
itud
e
MJD/14.898-X
Interesting Stars: Plateau Stars12.5
13
13.5
14
14.5
150 0.2 0.4 0.6 0.8 1
Star 317 Phase Diagram
ma
gn
itud
e
MJD/367.64 - X
13
13.5
14
14.5
15
15.5
160 0.2 0.4 0.6 0.8 1
Star 1223 Phase Diagram
ma
gn
itud
e
MJD/389.61 - X
13.5
14
14.5
15
15.5
160 0.2 0.4 0.6 0.8 1
Star 1495 Phase Diagram
ma
gn
itud
e
MJD/394.73 - X
15
16
17
18
19
202500 2600 2700 2800 2900 3000
Star 1654 Lightcurve
ma
gn
itud
e
MJD-2452800
Interesting Stars: SAS Stars14.6
14.8
15
15.2
15.4
15.6
15.8
16
16.20 500 1000 1500 2000 2500 3000
Star 1007 Lightcurvem
ag
nitud
e
MJD-2452800
11
11.2
11.4
11.6
11.8
12
12.20 500 1000 1500 2000 2500 3000
Star 82 Lightcurve
ma
gn
itud
e
MJD-2452800
Define Short-term Photometric Resolution (STPR) as for a Gaussian fit to a histogram of several hundred signal measurements for a given star and Long-term Photometric Resolution (LTPR) as for the nightly average signal measure of a given star over an entire campaign.
0.01
0.1
100 1000 104
105
M23 Data
Stellar 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.
Functional fits shown of form: STPR=[(C1)² + (C2signal-1/2)² + (C3signal)2]1/2
0.01
0.1
1
100 1000 104
105
106
107
LTPR vs Mean Stellar Signal (M23)
Mean Signal (ADU)
0
2
4
6
8
10
12
14
16
0 0.05 0.1 0.15
M23 Summer 2011
Standard deviation of nightly signal over mean signal
0.001
0.01
0.1
10 100
Flux Resolution vs. Altitude
Altitude (degrees)
8
10
12
14
16
0 1 2 3 4 5 6 7
M23 Color-Magnitude Diagram
Non-VariableHA Pulsating StarsLA Pulsating StarsEclipsing Binaries
I
AVG R-I
8
10
12
14
16
0 1 2 3 4 5 6 7
M23 Color-Magnitude Diagram
Non-VariableHA Pulsating StarsLA Pulsating StarsEclipsing Binaries
I
AVG R-I
Star 16
Star 41Star 69
Star 519
Star 166
Star 1267
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.