Shashi M. Kanbur
September 2010
Results
 In 5 years, > 21 papers in the two leading peer reviewed




journals in Astrophysics (Astrophysical Journal,
Monthly Notices of the Royal Astronomical Society).
No course release.
5 papers with undergraduate co-authors.
Worked with about 30 undergraduates on research
projects.
About 30 presentations at regional, national and
International conferences.
2006 Chretein award of the American Astronomical
Society.
Collaborators
















Chow Choong Ngeow, NCU, Taiwan.
Lucas Macri, Texas A&M.
Douglas Leonard, SDSU.
Ata Saradjeni, University of Florida.
Martin Hendry, University of Glasgow, UK.
Niall Tanvir, University of Leicester, UK.
Robert Szabo, Konkoly Observatory, Hungary.
Chris Koen, University of Witwatersand, S. Africa.
Antonio Kanaan, UFSC, Brazil.
Anil Pradhan, Ohio State
Marcello Marconi, Naples Observatory, Italy
Amplavanar Nanthakumar (Oswego)
Steven Reyner (Oswego)
Robert Buchler (University of Florida)
Hilding Nielson (University of Bonn)
Elio Antonello (Merate Observatory - Italy)
Students
















Gregory Feiden (Dartmouth)
Dylan Wallace (University of Alaska)
Daniel Crain (Clarkson)
Sean Scott (SUNY Binghampton)
Jim Young (RPI)
Frank Ripple (University of Massachusetts
Robin Dienhoffer (University of Virginia)
Earl Bellinger
Joshua Primrose
Joshua Brown (UofR)
Dennis Quill
Martin Berke
Anna Bontorno
Joe Bennett
Danielle Citro
Lillie Ghobrial
Jill Neeley (Ithaca College)
Matthew Turner (Rice)
Isaac Richter (UofR)
Tim de Haas (UofR)
Alex James (SUNY Geneseo)
Eamonn Moyer (SUNY Genseo)
Brandon Gilfus
Peter Thompson (University of Rochester)
Adam Biesenbach (Wall Street)
Sid Meyers
Stephanie Magin
Jessica Halsey
Samantha Hoffman (Texas A&M)
Michael Evans
Variable Stars
 Intrinsic variation, well defined period of oscillation.
 Regularly repeating brightness variations – light curve.
 Physics of this is reasonably well understood.
 Cepheids: pop I, young, high metallicity, in galactic
disk, crucial importance for the extra-galactic distance
scale.
 RR Lyraes: pop II< old, low metallicity, in globular
clusters in galactic halo, important as secondary
distance indicator and for age determinations.
PL relation








m: apparent magnitude
M: absolute magnitude
m-M = distance modulus
m-M = 5log(d) -5
M = a + blogP
Extra-Galactic Distance Scale
V=H0 x d
Know H0 to 1% accuracy imples knowledge of the
equation of state for dark energy.
 PL relation related to PC relation.
Multiphase Cepheid PC/PL Relations in the
LMC/SMC using OGLE III data
 Cepheid Period-Luminosity (PL) relation is one of the
most fundamental relations in Astrophysics.
 M = a + b log P
 At mean light.
 Its not linear! Two distinct relations.
 Formulate a relation between log P and magnitude at
different phases of pulsation.
 New window onto stellar pulsation. Permits a detailed
comparison with models.
Multiphase Movies:
 http://www.oswego.edu/~kanbur/IRES2009/Vphase.mov
 A great deal of things to understand here. Not scratched the surface







yet.
Color is the difference between two magnitudes.
Period-Color relations as a function of phase
http://www.oswego.edu/~kanbur/IRES2009/Cphase.mov
Definitive evidence of sharp nonlinearity.
New tool to constrain theoretical models of stellar pulsation.
Comparison with models
http://www.oswego.edu/~kanbur/IRES2008/keele.ppt
Random Walk Methods








Ei = Vi - a - b.logPi
Order according to period: P1<P2<P3<…..
Partial Sums of residuals:
C(j) = Σ(V k - a – blogPk) = Σrk
If no deviations from linearity, C(j) is a random walk.
Define R = max[C(j)] – min[C(j)]
For linearity, R will be close to zero.
Permute rk, find R for the permutation, repeat for a large
number of permutations, determine the fraction of
permutation R-values which exceeds the observed value –
the significance level of observed R.
 Bootstrap
Results
 http://www.oswego.edu/~kanbur/IRES2010/poster.pdf
 http://www.oswego.edu/~kanbur/IRES2010/poster2.p
df
 http://www.oswego.edu/~kanbur/citro.pptx
 LMC Wessenheit function is nonlinear
 SMC Wessenheit function is nonlinear
 SMC PL relation nonlinear at periods around 2 days.
 How do these multiphase relations vary with
metallicity?
 http://www.oswego.edu/~kanbur/IRES2010/typeI.pdf
New Statistical Methods
 With Amplavanar Nanthakumar.
 Detecting nonlinearity:
 Break into small segments. Compare slope of nth
segment with that of an “average” of all the previous
segments.
 Testimator: generalized this to n>2 (Kanbur et al 2007,
2008.
 Testimator : to check for heteroskedasticity: variance
of nth segment compared to an “average” of the
variance of the previous segments.
New InfraRed Observations of LMC
Cepheids
 http://www.astro.umontreal.ca/cpapir/index_en.html
 Competetive applications for telescope time.
 Obtained time in 2006/2007/2008 at NOAO facilities
in Chile using queue scheduled observations.
 Data worked on by Daniel Crain, Frank Ripple.
 Over 300GB of raw data. A major new dataset. Would
be ideal for a PhD project/post-doc project.
 IR counterpart of the OGLE II/III project.
 Very useful for other researchers.
Results
 http://www.oswego.edu/~kanbur/citro.pptx
PlotPourri
 http://www.oswego.edu/~kanbur/IRES2010/pp.pdf
IRAC bands PL Relation
CFHT Observations
CFHT Observations
 Authors: Samantha Hoffmann (Texax A & M), Lucas Macri (Texax A & M), Chow-Choong
Ngeow
(NCU), Shashi Kanbur (SUNY-Oswego)
Abstract:
NGC 4258, a nearby (D=7.2Mpc) spiral galaxy, serves as the "anchor" or first rung in the
Extragalactic Distance Scale thanks to a very precise and accurate geometric distance
estimate based on maser observations. We have imaged NGC 4258 with Gemini from 2004 to
2007 and discovered a large number of long-period Cepheids, extending the upper period
range of the previously-existing HST Period-Luminosity (P-L) relation from 45 to 150
days. In addition, we discovered numerous long-period variables (LPVs) with periods up
to 900 days. These variables have the potential to be excellent distance indicators in
the near-infrared, which is highly relevant for the JWST era. Queued observations of NGC
4258 with CFHT have been carried out in 2010A Semester, for a total of 4 hours. Our CFHT
observations will be used to (i) obtain more robust periods for the variables and
provide updated phase information in support of ongoing HST observations at H band; (ii)
carry out a search for ultra-long period Cepheids in this galaxy; (iii) tie the existing
Gemini observations to the Sloan magnitude system, to obtain accurate magnitudes and
colors for these important variables. We present preliminary results for the study of
Cepheids and long period variables in NGC 4258 based on the Gemini and CFHT data.
Theoretical Models
Galactic Globular Clusters and the
Oosterhoff Dichotomy
M3/M15:
PC/AC Relations using existing data
 Period-Color and Amplitude Color Relations at max/min
light.
 RR Lyraes in OoII clusters thought to be more evolved than
RR Lyrae clusters. This is seen to some extent in PeriodColor and Period-Amplitude relations at mean light.
 Analyzing existing data at maximum and mean light
demonstrates this also occurs for PC relations at max light.
 Observing campaign in April 2010 yielded significant new
data for other globulars in the Galaxy – currently being
analyzed.
Simulating RR Lyrae light curves
 Not theoretical modeling ‘filling in gaps between observed






data.’
Getting an observed light curve which captures reality
without too much ringing and with as few parameters as
possible.
Fourier analysis.
Principal Component Analysis (Kanbur et al 2002).
Cubic Splines.
With Steve Reyner.
Cubics (ie without requiring continuity of the derivative).
RR Lyrae Stars in M31/Sloan RR
Lyraes
 M31 nearby spiral galaxy.
 Reanalyzed data from a sample of 55 RR Lyrae stars in M31.
 2 new multiperiodic variables using the cubic polynomial




method.
Possible indications of ‘ modal interaction’.
Analyze new data set.
Sloan Digital Sky Survey. Analysis of RR Lyraes reveals
interesting Period-Color Relation Behavior.
Interaction of the hydrogen ionization front and stellar
photosphere.
The Robotic Telescope
 http://www.oswego.edu/~kanbur/IRES2008/IRES2008
.html
 http://www.oswego.edu/~kanbur/IRES2009/IRES2009
.html
 http://www.oswego.edu/~kanbur/IRES2010/IRES2010.
html
The Opacity Project
 Stellar Opacity: resistance to flow of radiation.
 Due to a number of atomic




absorption/scattering/emission processes.
The opacity as a function of temperature and density is
a vital component of stellar evolution/pulsation
calculations.
Stellar Evolution: cornerstone of modern Astrophysics.
1980: Cepheid Bump Mass Discrepancy – is the
Rosseland Mean Opacity the culprit.
1992: Yes!
The Opacity Project Revisited
 But many approximations in OP R matrix calculations due to







computer resources of the time.
Detailed NLTE radiative transfer calculations try to match
observed solar spectrum.
Can only do this with significantly reduced solar abundances
(CNONe).
This upsets helioseismology.
Is a further opacity revision the solution to the problem?
Preliminary calculations suggest a revision of OP opacities by
about 10-50% at those abundances mandated by NLTE radiative
transfer calculations.
This revision of opacities aleviates the helioseismology problem.
But whats the effect on stellar pulsation/evolution?
Watch this space!