High-Cadence, Long-Baseline Light Curves of Red Giant Variable Stars Robert Arnold1, Joshua Pepper2, Joseph Rodriguez3, and the KELT Collaboration

1 University of Central Arkansas 2 Lehigh University 3 Vanderbilt University

Link to

poster

PDF

Miras are variable Asymptotic Giant Branch (AGB) stars,

with large amplitude changes and periodic or

semiperiodic behavior over long time spans (>100

days). We used observations from the KELT photometric

survey for transiting exoplanets, along with public

catalogs, to identify previously unknown large amplitude

AGB variables, including Miras.

KELT is a wide-field, small aperture photometric survey

for transiting planets orbiting bright stars. The survey

uses two fully robotic telescopes, one in Arizona and one

in South Africa, to survey roughly 60% of the sky. The

goal of the survey is to discover exoplanets transiting

stars brighter than those typically observed by other wide-

field transit surveys, but fainter than those stars

comprehensively searched by RV surveys – a target

magnitude regime of 8 < V < 10. However, KELT

acquires light curves of stars over the range of 7 < V <

13. KELT began regular operations in 2005, and thus has

over 9 years of baseline observations on the longest

observed fields. The unique combination of baseline,

cadence, and photometric precision (~1% for stars

8<V<10) of the KELT dataset provides the ability to

perform research in a variety of different fields of stellar

astrophysics. Here we use the KELT data set to study the

photometric variability of AGB stars. For more information

on the KELT dataset, see Pepper et al. 2007.

.

Identification of Variable Red Giants • Computation of Stetson analysis to search for coherent

variability

Filtered stars with Stetson L statistic > 5.0

• Computation of Lomb–Scargle periodogram to

determine periodicity

Filtered stars with Lomb-Scargle SNR > 80

• Of 2 Million KELT Objects, 21279 Possible AGBs

• 3210 with L Statistic > 5.0

• Of those, 300 with Lomb-Scargle SNR > 80

Fig. 1 and Fig. 2: The Telescopes used in the KELT survey. The

KELT North Telescope is shown on the left and is located at

Winer Observatory near Sonoita, Arizona. The KELT South

Telescope is on the right and is located at the SAAO observing

station near Sutherland, South Africa.

Fig. 2: Two-color diagram used in study. Locus of AGB

stars (shown in red) in lined region

Fig. 3: Location of AGB stars (shown in red) in the

KELT survey.

Fig. 5: A KELT light curve (left) for an AGB star with a regular period of 274.3 days and a well established

amplitude. The light curve consists of 3748 data points. The phased KELT data is shown on the right.

• Lomb, N.R. 1976, A&SS, 39, 447

• Pepper, J., Kuhn, R.B., Siverd, R., James, D., Stassun, K. 2012, PASP, 124, 230

• Pepper, J., Pogge, R. W., DePoy, D.L., Marshall, J.L. et al. 2007, PASP, 119, 923

• Press, W.H. & Rybicki, G.B. 1989, ApJ, 338, 277

• Press, W.H., Teukolsky, S.A., Vetterling, W.T. & Flannery, B.P. 1992, Numerical Recipes in C, 2nd ed. (New

York: Cambridge University Press)

• Scargle, J.D. 1982, ApJ, 263, 835

• Stetson, P.B. 1996, PASP, 108, 851

• Tu, X., Wang Z.-X. 2013, Research in Astronomy and Astrophysics, 13, 323

Introduction

KELT: The Kilodgree Extremely Little Telescope

Methods

Fig. 6: A KELT light curve (left) showing an AGB star with regular period of 191.1 days but a changing amplitude. The maxima

fluctuate between 9.7 V to 10.5 V. The light curve consists of 4984 data points. The phased KELT data is shown on the right.

Fig. 7: A KELT light curve showing an AGB star with a primary period of 69.1 days and a long secondary period (LSP) of

560.4 days. The light curve consists of 5740 data points. The phased KELT data is shown on the right.

Acknowledgments This research was supported by the Lehigh University Research Experiences for Undergraduates (REU) program through National Science Foundation grants PHY-0849416 and PHY-1359195.

Identification of Asymptotic Giant Branch

Stars • Cross-match KELT Objects with WISE and 2MASS

Catalogs

• Locus For AGBs From Tu & Wang (2012)

Used K-W3 vs. J-K Color Cuts

Results

Acknowledgments

References

Link to

KELT-North

website