Discovering Cepheid and RR Lyrae Stars:
Pan-STARRS Science Archive @ STScI and Robotically Controlled Telescopes
Elizabeth Johnson
Villanova University
Advisor: Lou Strolger
Armin Rest (STScI), Richard I Anderson (JHU), Annalisa Calamida (NOAO),
Scott Engle (Villanova), Ori Fox (STScI), David Laney (WKU)
Background
Nature 2014
Feast et al.
• Goal: identify and produce light curves for thousands of previously
unidentified Cepheid and RR Lyrae stars
• Cepheid and RR Lyrae stars:
• Important markers in the cosmic distance ladder (Period-Luminosity
Relation)
• Useful in studying galactic structure and stellar ages
More on Cepheid and RR Lyrae Stars
• Radially Pulsating
• Period Luminosity Relationship
Method for
Candidate Selection
Color:
Classical Cepheids
Sesar et al.
Variability:
•
RR Lyrae Variables
Random Stars (PS1 SAS)
Color Selected Stars in
Green (PS1 SAS)
RR Lyrae Stars in Red (from Catalina
Survey… matched to stars in PS1 3pi)
MAD Evaluation
•
•
1% of all color-selected stars fall above the grey
75% of RR Lyrae stars fall above the grey
RR Lyrae Candidates PS1 3pi (blue
triangles)
What’s Happening Now: Observations
•
•
•
•
1.3 m RCT telescope (Kitt Peak)
Nightly observations
3 exposures/night
Observing a known Ceph and
known RR Lyr
• Observing new candidates from
PS1
Eventually:
• Modify observing strategy so
we catch different cadences of
variation
Results: Known Cepheid
PS1VKCE3294708+561639
V* CP Cep
Results: Known RR Lyrae Star
PS1VCRR2554999+593014
LINEAR 19902731
Results: Possible Cepheid
PS1VCRR3387909+320002
Results: Non-Variable Star and
Possible UV Ceti (Flare Type)
Variable
PS1VCCE2690344+320817
PS1VCCE2966097+320634
NSV 24882
Next Steps:
RATIR Telescope
Researchgate.net
Watson et al.
• Prepare/improve selection technique for use with
the upcoming ps1 3pi final catalog
• Create a semi-automated process to get from catalog
candidates, to observations, to light curves and
identification continuing into the fall
• >10,000 new variables, Cepheids, and RR Lyrae stars