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\IBVShead{5348}{4 December 2002}

\IBVStitle{HD 67852:  A New {\large \boldmath $\delta$}~Scuti Variable}

\IBVSauth{HENRY$^{1,2}$, G. W.}

\IBVSinst{Center of Excellence in Information Systems, Tennessee State University, 330 10th Ave. North, Nashville, Tennessee  37203, U.S.A.; e-mail: henry@schwab.tsuniv.edu}

\IBVSinst{Senior Research Associate, Department of Physics and Astronomy,
Vanderbilt University, Nashville, TN  37235}

\SIMBADobj{HD 67852}
\IBVStyp{ DSCT }
\IBVSkey{photometry}


\begintext

The early-F star HD~67852 was used as a photometric comparison star with 
the T8 0.8~m automatic photoelectric telescope (APT) at Fairborn 
Observatory\footnote{For further information on Fairborn Observatory see 
{\tt http://www.fairobs.org}.} in our program to follow brightness changes in a 
large sample of solar-type stars (Baliunas et al.  1998; Henry 1999).  It 
was recognized as a low-amplitude variable from 51 Str\"{o}mgren $by$ 
observations in the 2000--2001 observing season and placed on the observing 
menu of the T3 0.40~m APT at Fairborn the next year to obtain additional 
Johnson $BV$ measurements. 
 
Very little is known about HD~67852.  Olsen (1979) estimated it to be either 
a reddened Ap star, a $\lambda$~Bootis star, or, less plausibly, a field 
horizontal branch star, based on its Str\"{o}mgren indices.  Gray (1989) 
obtained a spectrum and classified it as F0 Vn, noting that it was broad-lined 
and possibly somewhat metal-weak.  The {\it Hipparcos} satellite made 64 
photometric measurements and found no variability (ESA 1997).  The 
{\it Hipparcos} mean $V$ = 7\fmm72, $B-V$ = 0\fmm245, and parallax of 0.00845 
arcseconds place the star on the main sequence near the middle of the 
$\delta$~Scuti instability strip.  Garc\'\i a-S\'{a}nchez et al. (2001) 
found HD~67852 to be one of 156 stars that have passed or will pass closer 
than five parsecs to the Sun within $\pm$10 Myr of the present; their results 
show the star encountered the solar system about 4.3 Myr ago at a heliocentric 
distance of 2.9 pcs.  By the {\it Hipparcos} epoch, the star had moved out 
to a distance of 118 pcs and continues to recede from the Sun with a radial 
velocity of 26~$\pm$~7 km~s$^{-1}$ (Garc\'\i a-S\'{a}nchez et al. 2001).
  
In this paper, I analyze the $\sim$360 Johnson $BV$ observations obtained 
with the T3 APT between 2001 September and 2002 May.  The data acquisition, 
reduction, and analysis methods, incorporating the method of Vani\^{c}ek 
(1971), have been described in Henry et al. (2001).  The photometric 
observations were made differentially with respect to HD~66950 ($V=6\fmm40$, 
$B-V=1\fmm06$, K0) as the comparison star and HD~65123 ($V=6\fmm35$, 
$B-V=0\fmm51$, F6~V) as a check star.  The check minus comparison ($K-C$) 
differential magnitudes were constant to 0.006 and 0.007 mag (standard 
deviation) in $B$ and $V$, respectively, which is close to the limit of 
precision for the T3 APT.  The variable minus comparison ($V-C$) differential 
magnitudes had standard deviations of 0.013 and 0.011 mag in $B$ and $V$, 
respectively, indicating definite variability in HD~67852.  The individual 
photometric observations are available on the Tennessee State University 
Automated Astronomy Group web site\footnote{See 
{\tt http://schwab.tsuniv.edu/papers/ibvs/hd67852/hd67852.html}.}.
  
An important feature of the Vani\^{c}ek technique is its ability to find 
multiple periods without prewhitening.  Power spectra of the ($V-C$) and 
($K-C$) differential magnitudes in both the $B$ and $V$ passbands were 
computed with the Vani\^{c}ek method over the frequency range 
0.01--50 day$^{-1}$, which corresponds to the period range 0.02--100 days.  
No evidence for periodic variability in the ($K-C$) observations was found, 
confirming the suitability of the comparison and check stars as photometric 
references.  The results for the ($V-C$) observations in $B$ are given in 
Figure~1, which has been truncated at a frequency of 20~day$^{-1}$ since no 
variability at higher frequencies was found.
  
\IBVSfig{12cm}{5348-f1.eps}{Power spectra of the HD~67852 Johnson $B$ 
observations obtained with the T3 APT.  The top panel reveals the strongest
frequency at 11.3027 day$^{-1}$.  With that frequency fixed, the power 
spectrum in the middle panel was computed, revealing a second frequency at
10.3756 day$^{-1}$.  The power spectrum in the bottom panel was computed
with the first two frequencies fixed and reveals no additional frequencies.}

Two frequencies were detected, corresponding to periods of 0.088474 and 
0.096380~days.  The peak-to-peak amplitudes in $B$ were 23.3 and 15.7 mag, 
respectively.  As can be seen in the middle panel of Figure~1, the 
identification of the second frequency is somewhat ambiguous; it and its 1-day 
alias have similar reduction factors.  Therefore, it is possible that 
11.377 day$^{-1}$ is the correct second frequency.   Essentially the
same results were obtained with the $V$ dataset.  The results are summarized 
in Table~1.  The $B/V$ amplitude ratios for the two periods are 1.46 and 
1.63, respectively.  The times of minimum in the two passbands agree within 
their errors for both periods.
  
\clearpage

\vskip 0.5cm
\centerline{Table 1. Photometric Analysis of HD~67852.}
\vskip 3mm
\begin{center}
\begin{tabular}{ccccccc}
\hline
            &           &              &        & Peak-to-Peak &                     \\
Photometric & $N_{\rm obs}$ & Frequency    & Period & Amplitude    & $T_{\rm min}$           \\
Band        &           & (day$^{-1}$) & (days) & (mmag)       & ($HJD - 2,450,000$) \\
\hline
$B$ & 371 & 11.3027     & 0.088474       & 23.3      & 2,300.031   \\
    &     & $\pm$0.0003 & $\pm$ 0.000002 & $\pm$ 1.5 & $\pm$ 0.001 \\
    &     & 10.3756     & 0.096380       & 15.7      & 2,300.081   \\
    &     & $\pm$0.0002 & $\pm$ 0.000002 & $\pm$ 1.7 & $\pm$ 0.002 \\
$V$ & 358 & 11.3028     & 0.088474       & 16.0      & 2,300.030   \\
    &     & $\pm$0.0002 & $\pm$ 0.000002 & $\pm$ 1.3 & $\pm$ 0.001 \\
    &     & 10.3750     & 0.096386       & 9.6       & 2,300.082   \\
    &     & $\pm$0.0002 & $\pm$ 0.000002 & $\pm$ 1.5 & $\pm$ 0.002 \\
\hline
\end{tabular}
\end{center}
\vskip 0.5cm

The $B$ observations are plotted in Figure~2, where they have been phased
with the two periods and computed times of minimum from Table~1.  To
render the low-amplitude variability more evident, the observations in each
panel have been prewhitened to remove the other period.  The photometric
variations at both periods closely approximate sinusoids.

\IBVSfig{9cm}{5348-f2.eps}{The Johnson $B$ photometry phased with the two
detected periods and times of minimum from Table~1.  The observations are
phased with the 0.088474-day period in the top panel and with the
0.096380-day period in the bottom panel.  In each case, the data have been
prewhitened to remove the other period.}

The majority of known $\delta$~Scuti variables are Population~I objects 
pulsating with low amplitudes in nonradial $p$ modes (Breger 2000).  
The catalog of Rodr\'{\i}guez et al. (2000) shows that nearly 30\% of the 
636 known $\delta$~Scuti stars have amplitudes smaller than 0.02~mag, which
implies that many more low-amplitude variables are yet to be discovered.
The high-amplitude $\delta$~Scuti stars (HADS) and the Population~II
SX Phe subgroups have much higher photometric amplitudes of 0.3 mag or
more (Breger 2000).  As seen in Figure~5 of Rodr\'{\i}guez et al. (2000), 
the high-amplitude stars have low rotational velocities 
($v\sin i < 20$~km~sec$^{-1}$), while the low-amplitude stars rotate much 
more rapidly.  HD~67852 clearly belongs to the more common low-amplitude, 
rapidly-rotating subgroup of $\delta$~Scuti variables.

Astronomy with automated telescopes at Tennessee State University is
supported through NASA grants NCC5-96 and NCC5-228 as well as
NSF grant HRD-9706268.

\references

Baliunas, S. L., Donahue, R. A., Soon, W., \& Henry, G. W., 1998, {\it ASP Conf. Ser.}, {\bf 154}, 153, The 10th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, ed. R. A. Donahue \& J. A. Bookbinder (San Francisco: ASP)
% Changed : Tue May 31 17:25:47 MEST 2005

Breger, M., 2000, {\it ASP Conf. Ser.}, {\bf 210}, 3, Delta Scuti and Related Stars, eds. M. Breger \& M. H. Montgomery (San Francisco: ASP)
% Changed : Tue May 31 17:25:47 MEST 2005

ESA. 1997, the {\it Hipparcos} and Tycho Catalogues (ESA SP-1200; Noorwijk: ESA)

Garc\'\i a-S\'{a}nchez, J., et al., 2001, {\it A\&A}, {\bf 379}, 634

Gray, R. O., 1989, {\it AJ}, {\bf 98}, 1049

Henry, G. W., 1999, {\it PASP}, {\bf 111}, 845

Henry, G. W., Fekel, F. C., Kaye, A. B., \& Kaul, A., 2001, {\it AJ}, {\bf 122}, 3383

Olsen, E. H., 1979, {\it A\&AS}, {\bf 37}, 367

Rodr\'\i guez, E., L\'{o}pez-Gonz\'{a}lez, M.\ J., \& L\'{o}pez de
        Coca, P., 2000, {\it A\&AS}, {\bf 144}, 469

Vani\^{c}ek, P., 1971, {\it Ap\&SS}, {\bf 12}, 10

\endreferences


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