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\input ibvs2.sty

\begin{document}
\IBVShead{5201}{20 November 2001}

\IBVStitle{The period of LV Herculis revisited}


\IBVSauth{TORRES, G.$^1$; LACY, C.\ H.\ S.$^2$; GUILBAULT, P.\ R.$^3$; DIETHELM, R.$^4$; BALDWIN, M.\ E.$^5$; LUBCKE, G.\ C.$^6$}

\IBVSinst{Harvard-Smithsonian Center for Astrophysics, 60 Garden St.,
Cambridge, MA 02138, USA, e-mail: gtorres@cfa.harvard.edu}
\IBVSinst{Department of Physics, University of Arkansas, Fayetteville,
AR 72701, USA, e-mail: clacy@comp.uark.edu}
\IBVSinst{P.O. Box 287, Chepachet, RI 02814, USA, e-mail: pete1199@aol.com}
\IBVSinst{BBSAG, Rennweg 1, CH-4118 Rodersdorf, Switzerland, e-mail: diethelm@astro.unibas.ch}
\IBVSinst{8655 N.\ Co.\ Road 775 E, Butlerville, IN 47223, USA,
e-mail: mbald00@hsonline.net}
\IBVSinst{3817 Patrick Henry Way, Middleton, WI 53562, USA, e-mail: gil2@ix.netcom.com}
	
\SIMBADobjAliasJ2000{LV Her}{TYC 2076 1042 1}{17 35 32.40 +23 10 30.6}
\IBVStyp{ EB }
\IBVSkey{photometry}

\IBVSabs{Continued spectroscopic observations of LV Her, in addition}
\IBVSabs{to new and archival times of minimum, have revealed that the}
\IBVSabs{true orbital period of this binary is 18.4359348(56) days.}

\begintext

In a recent note (Torres 2000) the orbital period of LV~Her (TYC~$2076-1042-1$;
\break  17\hr 35\mm 32\fsec4, +23\deg 10\arcm 31\arcs, 
J2000; SpT. F9, $V = 10.9$) was reported to be 18.13120 days based on
radial velocity measurements made at the Harvard-Smithsonian Center
for Astrophysics (CfA). This seemed to solve the long-standing mystery
about the true period of this binary, claimed originally to be
2.634~days by Zessewitsch (1944) and later revised to 5.2674 days by
Zessewitsch (1954).  It also seemed to solve the problem posed by the
preliminary spectroscopic orbit obtained by Popper (1996), with an
even longer period of 9.218 days. That orbit implied a total mass for
the system of only $\sim$1.0~M$_{\odot}$, which is too small for two
very similar main-sequence stars of spectral type F9 or G0 in an
eclipsing system. 

Although the new 18.13120-day period gave a good fit to the CfA radial
velocities, the report by Torres (2000) mentioned the lingering
difficulty that the ephemeris did not agree with the few published
times of minimum for LV~Her. Continued spectroscopic observations at
CfA eventually hinted at a problem with the orbit presented by Torres
(2000), as additional velocity measurements began to show large
residuals. In particular, new observations on the steeper portions of
the velocity curves that were not well covered by the original data
deviated considerably from the predictions. 

Photometric (CCD) observations in the visual band by one of us (CHSL)
with a robotic telescope at the Univ.\ of Arkansas also indicated
discrepancies in the times of eclipse compared to the ephemeris by
Torres (2000). It was soon found that a slight adjustment to the
period of about $+0.3$~days gave an excellent fit to all the
spectroscopic observations, as well as to the new and published
eclipse timings. 

Subsequently, numerous times of eclipse have been recovered from
archival photographic plates going back nearly a century that are
extremely valuable for confirming and improving the period of LV~Her.
Blue-sensitive patrol plates from the AC series at the Harvard College
Observatory were measured by PRG using a sequence of steps to estimate
changes in brightness. Similar material from the Sky Survey plates at
the Sonneberg Observatory was measured by RD. In addition, a number of
times of minimum have been derived from visual observations over the
last decade by MEB.  All of these observations are listed in Table~1,
along with the CCD measurements mentioned above and also the
historical times of minimum from the literature. A weighted
least-squares adjustment to these data was performed by adopting
typical uncertainties of 0.046~days and 0.012~days for the
photographic and visual minima (determined by iterations), 0.004~days
for the first two photoelectric minima, and 0.0008~days for the final
more accurate timing. The ephemeris obtained for LV~Her is:

\begin{center}
${\rm Min~I~} = 2,\!452,\!066.66949(95) + 18.4359348(56)\cdot E$ \\
${\rm Min~II} = 2,\!452,\!064.1673(29) + 18.4359348(56)\cdot E$.
\end{center}
 where the figures in parenthesis represent the uncertainty in the
last digits. Separate solutions for a period from the primary and
secondary minima show no evidence for apsidal motion. 

\vskip 0.5cm

\centerline{Table 1. Times of minimum for LV Her (HJD$-$2,400,000).}
%\vskip -2mm
\begin{center}
\begin{tabular}{l@{}c@{~}c@{~}rc@{~}c@{~~~}|l@{}c@{~}c@{~}rc@{~}c}
\hline
HJD  & Type$^1$  & Obs$^2$ & Cycle &   O$-$C   & Ref$^3$ & HJD  & Type & Obs & Cycle &   O$-$C   & Ref \\
%     &      &     &       & (days)  &     &      &      &     &       & (days)  &     \\
\hline
   15929.712  &  2 & pg & $-$1960 & $-$0.0231 & 1   &   37906.406  &  ? & pg & $-$768 & ($-$1.4956) & 4 \\
   16224.798  &  2 & pg & $-$1944 & $+$0.0879 & 1   &   38147.573  &  1 & pg & $-$755 & $+$0.0043 & 2 \\
   16669.658  &  1 & pg & $-$1920 & $-$0.0467 & 1   &   38587.449  &  2 & pg & $-$731 & $-$0.0500 & 2 \\
   17351.799  &  1 & pg & $-$1883 & $-$0.0353 & 1   &   40744.498  &  2 & pg & $-$614 & $-$0.0053 & 2 \\
   18605.473  &  1 & pg & $-$1815 & $-$0.0049 & 1   &   41060.502  &  1 & pg & $-$597 & $+$0.0556 & 2 \\
   23601.681  &  1 & pg & $-$1544 & $+$0.0648 & 1   &   41982.251  &  1 & pg & $-$547 & $+$0.0078 & 2 \\
   24062.505  &  1 & pg & $-$1519 & $-$0.0096 & 1   &   42664.347  &  1 & pg & $-$510 & $-$0.0258 & 2 \\
   26032.643  &  2 & pg & $-$1412 & $+$0.0156 & 2   &   46001.268  &  1 & pg & $-$329 & $-$0.0090 & 2 \\
   26032.644  &  2 & pg & $-$1412 & $+$0.0166 & 1   &   46941.483  &  1 & pg & $-$278 & $-$0.0266 & 2 \\
   26090.482  &  1 & pg & $-$1409 & $+$0.0146 & 2   &   47381.384  &  2 & pg & $-$254 & $-$0.0559 & 2 \\
   26219.577  &  1 & pg & $-$1402 & $+$0.0581 & 1   &   48100.425  &  2 & pg & $-$215 & $-$0.0163 & 2 \\
   26901.699  &  1 & pg & $-$1365 & $+$0.0505 & 1   &   48487.60   &  2 & v  & $-$194 & $+$0.0041 & 5 \\
   27212.514  &  2 & pg & $-$1348 & $-$0.0132 & 2   &   48508.60   &  1 & v  & $-$193 & $+$0.0359 & 5 \\
   27636.462  &  2 & pg & $-$1325 & $-$0.0917 & 2   &   48545.52   &  1 & v  & $-$191 & $+$0.0840 & 5 \\
   27657.429  &  1 & pg & $-$1324 & $-$0.0928 & 2   &   48745.70   &  2 & v  & $-$180 & $+$0.0010 & 5 \\
   28281.830  &  2 & pg & $-$1290 & $+$0.0186 & 1   &   48948.50   &  2 & v  & $-$169 & $+$0.0057 & 5 \\
   30254.522  &  2 & pg & $-$1183 & $+$0.0655 & 1   &   49098.540  &  1 & pg & $-$161 & $+$0.0260 & 2 \\
   31268.42   &  2 & v  & $-$1128 & $-$0.0129 & 3   &   49206.61   &  2 & v  & $-$155 & $+$0.0126 & 5 \\
   31289.35   &  1 & v  & $-$1127 & $-$0.0510 & 3   &   49667.49   &  2 & v  & $-$130 & $-$0.0058 & 5 \\
   31326.29   &  1 & v  & $-$1125 & $+$0.0171 & 3   &   49688.48   &  1 & v  & $-$129 & $+$0.0161 & 5 \\
   31342.16   &  2 & v  & $-$1124 & $-$0.0166 & 3   &   49925.65   &  2 & v  & $-$116 & $+$0.0511 & 5 \\
   34626.332  &  1 & pg &  $-$946 & $+$0.0268 & 2   &   52008.85   &  2 & pe &   $-$3 & $-$0.0095 & 6 \\
   37444.539  &  2 & pg &  $-$793 & $+$0.0680 & 2   &   52045.74   &  2 & pe &   $-$1 & $+$0.0086 & 6 \\
   37869.519  &  ? & pg &  $-$770 & ($-$1.5107) & 4   &   52066.6993 &  1 & pe &      0 & $-$0.0002 & 6 \\
\hline
\end{tabular}
\end{center}

\begin{tabular}{l p{13cm}}
{\small $^1$Type:} & {\small 1 = primary eclipse, 2 = secondary eclipse. }\\
{\small $^2$Obs:} & {\small pg = photographic, v = visual, pe = photoelectric. }\\
{\small $^3$Ref:} & {\small 1 = Guilbault (Harvard plates), 2 = Diethelm (Sonneberg plates), 3 = Zessewitsch (1954), 4 = Huth (1964), 5 = Baldwin (visual), 6 = Lacy (CCD) }\\
\end{tabular}


\vskip 0.5cm

Only the two photographic timings by Huth (1964) give large residuals
of $\sim$1.5~days (indicated in parentheses in the table), and were
not included in the fit. Inspection of the original plates from the
Sonneberg Observatory by one of us (RD) revealed an anomalously bright
comparison star on both dates (which is possibly variable) as well as
a plate defect on the second date, which make these measurements
highly suspect. 

The large eccentricity ($e = 0.61$) and peculiar orientation of the
orbit of LV~Her result in a secondary minimum that does not occur
midway in phase between two primary minima, but instead at phase
$0.8626 \pm 0.0032$. The separation of only 0.137 from the primary
eclipse has no doubt contributed to the confusion of the early
observers and to the difficulty in establishing the period. The new
value, which is essentially double the period proposed by Popper
(1996), along with the spectroscopic observations from CfA implies
minimum masses of 1.20~M$_{\odot}$ and 1.17~M$_{\odot}$ for the
components, in good agreement with the spectral type. The apparently
synchronous rotation of the stars (see Torres 2000) and the eccentric
orbit make this system potentially very interesting for a comparison
with current theories of tidal evolution.  Spectroscopic observations
at CfA as well as photometric (CCD) observations are being continued,
and a detailed investigation of the binary will be the subject of
future paper. 

\vskip 0.5cm

PRG would like to thank Alison Doane, acting curator of the
Astronomical Photograph Collection at the Harvard College Observatory,
for the use of the plates. RD wishes to thank the administrative staff
of the Sonneberg Observatory for the hospitality provided during his
stay there. 
	
\references

Huth, H. 1964, {\it Mitt.\ Ver\"and.\ Sterne, Sonneberg}, Band 2, Heft
5, 112

Popper, D.\ M. 1996, {\it ApJS}, {\bf 106}, 133
% \BIBCODE{1996ApJS..106..133P}

Torres, G. 2000, {\it IBVS} 4971

Zessewitsch, V.\ P. 1944, {\it Astron.\ Circ.}, {\bf 36}, 5

Zessewitsch, V.\ P. 1954, {\it Odessa Report}, {\bf 4}, 113

\end{document}
