Search for Pulsations in Metal Deficient Field Giants

1
Search for Pulsations in Metal Deficient Field
Giants

• Emily Alicea-Muñoz
• University of Puerto Rico
• Mayagüez Campus
• Department of Physics

Advisor Andrea Dupree Mentor Jason
Aufdenberg Harvard-Smithsonian Center for
Astrophysics Solar and Stellar Physics Division
2
Outline

• Introduction and Goals
• Stellar Targets (8)
• Observations and Reduction Procedures
• Data and Results for Some Stars
• HD 232078
• HD 6833
• HD 29574
• Summary and Conclusions

3
Introduction

• Globular cluster red giants are thought to
  experience mass loss in their evolution along the
  red giant branch of the HR Diagram. (Iben
  Renzini 1983)

M5

• No such mass loss has ever been directly
  observed.

4
HR Diagram of globular cluster M5
brighter ?
Red Giant Branch
cooler ?
Ian Smail, URL http//www.phys.unsw.edu.au/astro/
wwwlabs/gcCm/gcCm\_intro.html)
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Introduction

• Emission wings around the Ha spectral region
  (l6562.808Å) of globular cluster giants have
  been interpreted as circumstellar material.
  (Cohen 1976)

• Asymmetries and time variations of these emission
  wings suggest chromospheric motions. (Dupree et
  al. 1984)

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Goals

• We would like to look at spectra of globular
  cluster red giants, but these stars require large
  telescopes and extended observing (Vgt12.38).
• We chose to study bright metal deficient field
  red giants as surrogates for globular cluster red
  giants.
• We hoped to find asymmetric, time-varying
  emission wings which would indicate chromospheric
  pulsations that could lead to mass loss.
• We also looked for Ha shifts that would also
  indicate chromospheric motions.

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Spectral line formation

• Optical depth t k Dh 1, where k is the
  line absorption coefficient and Dh is the depth.

• Therefore, Ha core is produced higher up in the
  chromosphere and the emission wings are produced
  deeper in the chromosphere.

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Emission wings
chromosphere expands
star
chromosphere contracts
star
(Hummer Rybicki 1968)
9
Stellar Targets

• Eight stars were chosen for spectroscopic
  analysis.
• Four of them have very low metallicities (with
  Fe/H abundances between -0.9 and -1.8), and the
  other four have even smaller metallicities (with
  Fe/H abundances between -1.92 and -2.6).
• My stars are cool ?
• (really Teff 4000 K).

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Stellar Targets
(POSS via Aladdin Previewer)
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M92 Fe/H -2.24 (Sandage 1970) 47 Tuc
Fe/H -0.76 (Hesser et. al. 1987)
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Observations and Reduction Procedures

• McMath-Pierce Main Telescope (NSO/Kitt Peak
  Observatory)
• Time Feb-May and Nov-Dec 1995 R l/Dl 43000
• IRAF software wavelength dispersion determined
  spectrum normalized Th-Ar lamp spectra used when
  needed

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Data and Results for Individual Stars
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HD 232078 ? Fe/H -1.54
Short wavelength (blue) emission wing
Long wavelength (red) emission wing
Normalized continuum level
Ha

• Spectra for this star showed photospheric lines,
  a strong Ha profile, and noticeable emission
  wings.

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HD 232078
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HD 232078
inflow
inflow
ratio (b/r)
velocity (km/s)
outflow
time (d)
time (d)

• Left ratio of emission wing intensities as
  function of time
• Right velocity of Ha with respect to the
  photosphere as a function of time
• Correlation between both plots
• At first, blue gt red ? inflow later, red gt blue
  ? outflow ? lower chromosphere moves
• At first, Ha vel gt 0 ? inflow later, Ha vel lt 0
  ? outflow much later, Ha vel gt 0 ? inflow again
  ? upper chromosphere pulsates
• Indicative of chromospheric pulsations with
  period P 50 d

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HD 6833 ? Fe/H -0.9

• Velocity plot of Ha core shows no pulsations.

• Spectrum shows Ha line, photospheric lines, and
  almost nonexistent emission wings

velocity (km/s)
time (d)
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HD 29574 ? Fe/H -1.92

• Sample spectrum. Notice how strong is the blue
  emission wing and how very tiny and almost
  nonexistent is the red emission wing.

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HD 29574
inflow
inflow
velocity (km/s)
ratio (b/r)
outflow
time (d)
time (d)

• Left ratio of intensities
• Right Ha velocity
• Notice the different patterns in the plots
• Star is experiencing chromospheric motions lower
  chromosphere falls upper chromosphere pulsates
• Pulsation period could not be determined.

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Comparisons

• Brighter stars are predicted to have emission
  wings dimmer stars are predicted to not show
  emission. (Smith Dupree 1988)

• We found that stars brighter than MV -1.8
  showed emission and pulsations, and stars dimmer
  than that did not.

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Summary, Conclusions and Future Work

• Spectroscopic analysis of the time variations of
  emission wings surrounding the Ha absorption core
  and velocity shift measurements of the core
  itself were performed for six metal deficient
  field red giants.

• In the near future analysis of data for HD
  110184 and HD 122563.

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Acknowledgments

• I would like to thank my advisor, Andrea Dupree,
  and my mentor, Jason Aufdenberg, for all their
  help and collaboration and everything theyve
  taught me during this summer.

Questions?