Spectrophotometry of Ap Stars

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Brandon Mitchell
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1 Spectrophotometry of Ap Stars ASTRA Status Report Barry Smalley Astrophysics Group Keele University Staffordshire United Kingdom

2 What is Spectrophotometry? Spectroscopy through a wide aperture No slit loses All stars in aperture give spectra Requires isolated stars

3 Why Spectrophotometry? Emergent fluxes from stars are shaped by many physical processes Absorption by atoms and molecules Turbulence and convection Pulsation and hydrodynamics High-precision measurements allow us to investigate these and other phenomena. Unfortunately, very little high-precision optical spectrophotometry exists.

atoms and molecules Turbulence and convection Pulsation and hydrodynamics

4 The ASTRA Team Automated Spectrophotometric Telescope Research Associates Science Saul Adelman (The Citadel) Austin Gulliver (Brandon University) Barry Smalley (Keele University) Instrument John Pazder (Dominion Astrophysical Observatory) Frank Younger (Aurora Astronomical Services) Telescope Lou Boyd & Don Epand (Fairborn Observatory)

University) Instrument John Pazder (Dominion Astrophysical Observatory) Frank

5 Fairborn Observatory Near Washington Camp, Patagonia Mountains, Southern Arizona. Lat: 31 23' 12'' N Long: ' 41'' W Alt: 1800m

6 The ASTRA Telescope Automated 0.5m f/8 Cassegrain slewing from star-to-star in <1 minute Declination coverage +80 to -30 Instrument aperture ~30 arcsec 1st order: 5500 ~ Å (13Å 2-pixel resolution) 2nd order: 3000 ~ 6000 Å (6.5Å 2-pixel resolution) Estimated sensitivity 5th mag. A0V star S/N>200 in 15 seconds ~10mag to 1% accuracy in ~1 hour

-30 Instrument aperture ~30 arcsec 1st order: 5500 ~ 10000 Å (13Å 2-pixel resolution)

7 Signal-to-noise Estimate

8 Instrument Overview Wavelength coverage: 3200 ~ 9500 Å Resolution: better than 15 Å Entire spectrum in one exposure using prism cross-disperser Minimum optical surfaces After alignment optical parts to be fixed Zeroth-order light for guiding Spectrum widened to ~5 pixels for optimal extraction

Minimum optical surfaces After alignment optical parts to be fixed

9 Inside the Spectrophotometer

10 Science CCD E2V CCD Alta system from Apogee Instruments Liquid cooled to about -60 C for science observations x 256 square 26-micron pixels.

11 Spectra Layout on Detector

12 Atmospheric Extinction Use 10 minutes every hour to observe secondary standards Determine atmospheric extinction Temporal variations Seeing variations

13 Absolute Flux Scale Vega will be the primary Flux Standard Accuracy to 1~2% ASTRA's Secondary standards compared to it ASTRA internal precision better than 1%.

14 Initial Observing Program Major Initial Projects Revision and Extension of the Secondary Standards Including those near selected variable stars Sample Fluxes of Population I and II Stars Auxiliary Projects Comparisons with Model Atmospheres Synthetic Colours and Line Indices from Spectrophotometry Collaborative Projects

of Population I and II Stars Auxiliary Projects Comparisons with Model

15 Collaborative Projects We want to work with interested astronomers in starting a variety of projects and getting initial results. We are particularly interested in those which find stellar parameters and/or study physical processes in stellar atmospheres. We are willing to obtain simultaneous as well as phase dependent observations. We will have a call for collaborative proposals once we know when scientific observations will begin.

We are particularly interested in those which find stellar parameters and/or study physical processes in

16 Some applications to Ap Stars Fundamental Parameters Using UV and IR fluxes and angular diameters Infrared Flux Method Comparison with model atmosphere predictions Precise measurement of flux variations Surface features Pulsations

Flux Method Comparison with model atmosphere predictions

17 Flux fitting Fitting model flux predictions to observed flux distributions Fit for both Teff and log g, simultaneously Sensitive to [M/H] and turb, especially cooler stars.

18 Magnetic Ap star: 53 Cam Spectrophotometry and Balmer lines discordant (Kochukhov et al., 2004) ASTRA can give continuous flux coverage Including the Balmer lines at modest resolution

19 Current Status Instrument in final stages of assembly So far every design specification has been met Taking test exposures Anticipate delivery to Fairborn in October Telescope construction well in hand Ready to mount the instrument Integration of telescope and instrument into automated system estimated 3~6 months. Begin to take observations of secondary standards

construction well in hand Ready to mount the instrument Integration of telescope and

20 Solar Spectrum with ASTRA The first test observation Saturday 12 August 2006! d e t a r b i l a c Un

21 Thank you! Contact us! Saul Adelman Austin Gulliver Barry Smalley For further Information

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