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Shashi M. Kanbur September 2010

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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 Chretein award of the American Astronomical Society.

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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)

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Students Gregory Feiden (Dartmouth) Jill Neeley (Ithaca College) Dylan Wallace (University of Alaska) Matthew Turner (Rice) Daniel Crain (Clarkson) Isaac Richter (UofR) Sean Scott (SUNY Binghampton) Tim de Haas (UofR) Jim Young (RPI) Alex James (SUNY Geneseo) Frank Ripple (University of Massachusetts Eamonn Moyer (SUNY Genseo) Robin Dienhoffer (University of Virginia) Brandon Gilfus Earl Bellinger Peter Thompson (University of Rochester) Joshua Primrose Joshua Brown (UofR) Adam Biesenbach (Wall Street) Dennis Quill Sid Meyers Martin Berke Stephanie Magin Anna Bontorno Jessica Halsey Joe Bennett Samantha Hoffman (Texas A&M) Danielle Citro Michael Evans Lillie Ghobrial

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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.

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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=H 0 x d Know H 0 to 1% accuracy imples knowledge of the equation of state for dark energy. PL relation related to PC relation.

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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.

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Multiphase Movies: 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 Definitive evidence of sharp nonlinearity. New tool to constrain theoretical models of stellar pulsation. Comparison with models

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Results df df 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?

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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, Testimator : to check for heteroskedasticity: variance of nth segment compared to an “average” of the variance of the previous segments.

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New InfraRed Observations of LMC Cepheids 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.

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Results

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PlotPourri

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IRAC bands PL Relation

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CFHT Observations

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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.

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Theoretical Models

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Galactic Globular Clusters and the Oosterhoff Dichotomy

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M3/M15:

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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 Period- Color 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.

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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).

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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.

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The Robotic Telescope html html

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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!

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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!

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