Semi-Regular Variable Star Population Semi-Regular Variable Star Population and Evolution Studiesand Evolution Studies

Jeff WilkersonJeff WilkersonDavid David

PfotenhauerPfotenhauerIowa Academy of Iowa Academy of

ScienceScience

April 18, 2015April 18, 2015

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 53 41,000 11 Feb. 2012 – 3 Oct. 2011

NGC 6514 (M23) 7.0 41 31,000 1 Mar. 2013 – 1 Oct. 2013

NGC 6514 (M23) 7.0 40 28,000 18 Feb. 2014 – 27 Sep. 2014

NGC 6514 (M23) 7.0 ? ? 1 Mar. 2015 – present

Student Participation:

Ujjwal Joshi

Nathan Rengstorf

Andrea SchiefelbeinTodd BrownBrajesh 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 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 SocietyLuther College HHMI

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 Timescales: a variance test

2

2

sec

nightsutivecon

longterm

14

14.1

14.2

14.3

14.4

14.5

14.6

14.70 500 1000 1500 2000 2500 3000 3500 4000

star600m

ag

nitu

de

CJD-2452800

13

13.5

14

14.5

15

15.5

16

16.50 500 1000 1500 2000 2500 3000 3500 4000

star1223

mag

nitu

de

CJD-2452800

13

13.5

14

14.5

15

15.5

16

16.52400 2600 2800 3000 3200 3400

star1223

ma

gn

itud

e

CJD-2452800

14

14.1

14.2

14.3

14.4

14.5

14.6

14.72400 2600 2800 3000 3200 3400

star600

ma

gn

itud

e

CJD-2452800

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

3/29 stars with periods < 270 days,

amplitudes > .8

10/20 stars with periods > 270 days,

amplitudes > .8

PopulationsPopulation Heterogeneity

RV Tau

1654

2510

Evidence of at least two major subpopulations

14

14.1

14.2

14.3

14.4

14.5

14.6

14.70 500 1000 1500 2000 2500 3000 3500 4000

star600m

ag

nitu

de

CJD-2452800

13

13.5

14

14.5

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15.5

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16.50 500 1000 1500 2000 2500 3000 3500 4000

star1223

mag

nitu

de

CJD-2452800

13

13.5

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14.5

15

15.5

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16.52400 2600 2800 3000 3200 3400

star1223

ma

gn

itud

e

CJD-2452800

14

14.1

14.2

14.3

14.4

14.5

14.6

14.72400 2600 2800 3000 3200 3400

star600

ma

gn

itud

e

CJD-2452800

Secular TrendsMean Magnitudes

Gaussian Fit of the Slope Values shows:

μ = 0.0086 ± 0.0019 mag/year

Additionally 34 of the 44 show positive slopes

0

2

4

6

8

10

12

14

-0.04 -0.02 0 0.02 0.04 0.06 0.08

44 SRV Light Curve Slope Histogram

# s

tars

Slope (mag/yr)

Mean = 0.0086 mag/yrStd. err. = 0.0019 mag/yr

μ3_3 = 0.0053 ± 0.0020 mag/year

μann= 0.0051 ± 0.0017 mag/year

μall = 0.0059 ± 0.0017 mag/year

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

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

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.

Secular TrendsData 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

14

14.1

14.2

14.3

14.4

14.5

14.6

14.70 500 1000 1500 2000 2500 3000 3500 4000

star600m

ag

nitu

de

CJD-2452800

13

13.5

14

14.5

15

15.5

16

16.50 500 1000 1500 2000 2500 3000 3500 4000

star1223

mag

nitu

de

CJD-2452800

13

13.5

14

14.5

15

15.5

16

16.52400 2600 2800 3000 3200 3400

star1223

ma

gn

itud

e

CJD-2452800

14

14.1

14.2

14.3

14.4

14.5

14.6

14.72400 2600 2800 3000 3200 3400

star600

ma

gn

itud

e

CJD-2452800

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

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.

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.