Download Spectral Variations of Several RV Tauri Type Stars Patrick Durant

Spectral Variations of Several RV Tauri Type Stars
Patrick
1South
1
Durant ,
S.B.
2
Howell ,
J.
1
Cash
and D.K.
1
Walter
Carolina State University, 2 National Optical Astronomy Observatory
ABSTRACT
DISCUSSION
Changing Spectra
We have examined the spectra of several RV Tauri type stars
including AC Her, SX Her and V Vul. As is typical of this
variable type, the stars show changes in spectral type and
line strength in addition to changes in their light curve over
time. Our group has acquired spectra of these stars during
the past 10 years using the coude feed telescope at Kitt Peak
National Observatory (KPNO). The set of spectra were
examined to determine their effective temperature and other
physical properties as a function of time. We present our
results which include the run of temperature and luminosity
variations vs. the star’s photometric behavior. Changes in
other physical parameters as a function of phase are also
discussed.
Significant changes in the spectra of SX
Her are shown here. On the left is a blue
spectrum from July 2003 showing a
relatively featureless continuum with
several absorption lines. On the right is
the same region of the spectrum almost a
year later in June 2004.
Balmer and
metallic lines are in emission, the
continuum has weakened and the calcium
H and K line profiles have changed.
AC Her
- steep rise in T in early phase of cycle
- factor of 3 increase in L in steep rise early in cycle
- data needed in later part of cycle to confirm steep
drop to lower values at the beginning of next cycle
SX Her
- nearly constant T over phase
- luminosity variation on the order of 20%
- radius change on the order of 10%
V Vul
- scatter of data makes conclusions uncertain
- rise in T during first half of cycle
- factor of 3 increase in L, at beginning of the cycle
Support for this work was provided by the NSF PAARE
program to South Carolina State University under award AST0750814. We thank the director of KPNO for his generous
allocation of telescope time in his project over the years.
FUTURE WORK
We are currently acquiring additional spectra for objects
already in our database as well as other RV Tauri and SemiRegular variables. Using the results of Nesmith and Cash
(adjacent poster, this conference), we will identify the
specific future Julian dates corresponding to data gaps in
phase space and obtain spectra on those dates.
RV TAURI STARS
 Pulsating variables with alternating deep and shallow
minima. See Nesmith & Cash (adjacent poster, this
conference) for examples of the light curves.
 Typical periods between successive deep minima are 30
to 150 days.
Future work will include error analysis of observed and
derived quantities as well as extinction corrections to our
observed magnitudes.
 Yellow supergiants which vary in spectral type from F to
G at maximum through K to M at minimum light
 Their evolutionary history is uncertain, but they occupy
the HR instability strip between the Cepheids and Miras
ANALYSIS
 We have acquired high signal to noise spectra of these
and other RV Tauri and Semi-Regular stars over the past
10 years using the coude feed telescope at KPNO
Plots of Stellar Quantities
The upper left plot shows the change of position of each star in the HR diagram
over time. Other plots show the change of T, L and R with respect to phase from
the light curve fits of Nesmith & Cash (adjacent poster, this conference).
• AC Her
Filled Triangle - V Vul
x SX Her
References
 Spectral types and luminosity classes were determined
by comparing our spectra to standards in the Jacoby
Spectral Atlas
 The effective temperature (T) was derived
spectral type
The ultimate goal of our 5-year study is to
determine the temporal change of the physical
parameters for RV Tauri stars throughout their
pulsation cycle in order to better understand the
physical nature of these objects.
AAVSO data, http://www.aavso.org
Hipparcos/Tyco data, http://simbad.u-strasbg.fr/Simbad
from the
Jacoby, G.H. et. al., 1984, ApJS. 56, 257.
 Photometric data were taken from the AAVSO dataset.
Light curve fits by Nesmith and Cash (adjacent poster, this
conference) were used to convert the Julian Dates of our
spectral observations to the appropriate phase of the
pulsation cycle
Nesmith, E. & Cash, J, 2010, Poster 417.15, this
conference
Percy, J. R. Understanding Variable Stars. New York, NY:
Cambridge University Press, 2007. pp. 1-80, 136-223
 The AAVSO data were used to determine the apparent
magnitude (m) on each date
 Stellar distances (d) were derived from the HipparcosTyco parallax database
 The absolute magnitude (M) was calculated using the
distance modulus:
m – M = 5log(d) – 5
 The luminosity (L) was then calculated from:
M(star) – M(sun) = –2.5log[L(star)/L(sun)]
 The stellar radius was calculated from L and T:
L(star)/L(sun) = [R2(star) x T4(star)]/[R2(sun) x T4(sun)]
 The variation of these quantities with phase was
examined
Acknowledgements
Range of Stellar Quantities Over the Phase Cycle
Star
T
M
(K)
(magnitudes)
AC Her 4900–6000 -2.17 to -3.37
SX Her 3900–3950 -0.16 to -0.56
V Vul 3150–4750 -1.63 to -3.03
L
(solar)
585–1761
91–132
352–1280
R
(solar)
30–41
21–25
43–73
Support for this work was provided by the NSF PAARE program to
South Carolina State University under award AST-0750814. We
thank the director of KPNO for his generous allocation of
telescope time over the years and the director of NOAO for his
support of this project.
We thank Dr. Kenneth Mighell, Director of the NOAO REU
program, for his support of this project.
We acknowledge with thanks the variable star observations from
the AAVSO International Database contributed by observers
worldwide and used in this research.