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\IBVShead{4219}{17 July 1995}

\centerline{\ft AF Sco -- A MIRA STAR, NOT A NOVA}
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AF Sco (= Harvard Variable 1108) is a poorly known object. It was 
first listed as a variable by Leavitt (1904). Swope (1932) published a 
finding chart, on which only the position of the star is indicated. 
Since it had not been seen (or rather re-observed) since the turn of 
the century, the 4th edition of the GCVS classified AF Sco as a nova. 
Some time ago, the Harvard plates were re-examined by B.~Fuhrmann 
(Sonneberg), who put a list of positive and negative observations at 
my disposal. The object had brightness maxima on 1896 May 14 
($m_{\rm pg} = 14.0$), 1897 June 4 (13.2) 1899 July 6 (12.2?), 1900 
September 5 (12.9) and around 1901 September 8 (13.3). 33 plates taken 
between 1902 mid-April and 1929 May, sometimes reaching limiting 
magnitude 17, do not show the star. An image of $m_{\rm pg} = 17.5$ 
is possibly visible on a plate taken on 1929 April 25.

The outburst image of the variable coincides with a quite bright star 
on the ESO/SERC plates, but the different times of Schmidt telescope 
observations make a determination of the colour impossible.

Spectroscopic observations (360 -- 700 nm), made on 1995 June 25
with EFOSC1 at the ESO 3.6m telescope show that AF Sco has a spectral
type M9 III, based on comparisons with spectrophotometric scans of
standard stars (Turnshek et al. 1985). The large range in magnitudes
on the Harvard plates ($m_{\rm pg}$ between 12.5 and 17.5) makes mira 
variability likely. From the brightenings observed between 1896 and 1901, 
a preliminary period of 388 days was derived. Making use of the 
fact that the star was not seen at the times when the later 
plates were taken, several trial runs with slightly different 
periods were made. The period that `avoids' times of maximum
light during observations made in later years leads to the preliminary 
light elements
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$t_{\rm max} = {\rm J.D.}~2414858 + 385 \times E \ \rm days$
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\noindent which should be improved by present-day observations.
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Previously, the object has been preliminarily identified with the 
IRAS source 16473--2528, and an IRAS spectrum is shown in Olnon
\& Raimond (1986). te Lintel Hekkert et al. (1991) have 
detected OH maser emission at 1612 MHz from it. The  
velocity separation $\Delta V = 10~\rm km/s$ and the period of 385 days
fits well into the trend in $\Delta V$ observed in mira variables of 
different periods and spectral types (Nguyen-Q-Rieu et al. 1979).
By comparing the IRAS flux of AF Sco at 12$\mu$m with normalized fluxes 
of miras in the period range 370\dots 400 days (Sivagnanam et al. 1988), 
we derive a distance estimate of $1300^{+600}_{-250}$~pc.
Using  period -- absolute magnitude calibrations (Duerbeck
\& Seitter 1982), we predict a visual magnitude at 
maximum between $m_{\rm vis} =$ 9.1 and 10.4 (neglecting interstellar 
absorption, which should be less than 1 magnitude). Thus the determination
of the precise period and an up-to date epoch of maximum light should be an 
easy task for amateur astronomers. A finding chart, based on the 
Digitized Sky Survey, is shown in Figure 1.

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Figure 1. The field of AF Sco. Its size is 4\farcm 5 $\times$ 4\farcm 5, north
is up and east to the left. The variable is marked with a circle.
Its coordinates are RA = 16\fh 50\fmm 25\fs,
Decl. $-$25\degr 33' 38'', in good agreement with the 
IRAS position  RA = 16\fh 50\fmm 25\fss 4,
Decl. $-$25\degr 33' 37'' (eq. J2000).
This image is based on a 4~minute exposure through a $V$-filter,
taken with the UK Schmidt on 1988 April 14.
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\large
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Summing up, the positional coincidence of the outbursting object with
the presently observed late type star confirm the IRAS identification,
and the observed light variations lead to a reclassification 
of AF Sco as a mira star.

Acknowledgements. 
I am grateful to B. Fuhrmann, who put his magnitude
estimates at my disposal, and to M. Naumann (ESO) 
for advice concerning the ESO/ST-ECF Online DSS.
This research has made use of the Simbad data base,
operated at CDS, Strasbourg, France. The finding chart is based on 
photographic data obtained using the UK Schmidt Telescope,
operated by the ROE, with funding from the UK SERC until 1988 June, 
and thereafter by the AAO.  Original plate material is \copyright{} the Royal
Observatory Edinburgh and the Anglo-Australian Observatory. The 
plates were processed into the present compressed digital form with 
their permission.  The Digitized Sky Survey was produced at the Space 
Telescope Science Institute under US Government grant NAG W-2166. 
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\beginauthors
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Hilmar W. DUERBECK
European Southern Observatory
Casilla 19001
Santiago 19, Chile
\endauthors

\references

Duerbeck, H.W., Seitter, W.C., 1982, pp. 216 and 218 in Landolt-B\"ornstein,
New Series, VI/2b (eds. H.H. Voigt and K. Schaifers), Berlin: Springer

Leavitt, H., 1904, {\it Harvard Obs. Circ.},  No.\,90

Nguyen-Q-Rieu, Laury-Micoulaut, C., Winnberg, A., Schultz, G.V., 1979, {\it A\&A}, {\bf 75}, 351

Olnon, F.M., Raimond, E., 1986, {\it A\&AS}, {\bf 65}, 607

Sivagnanam, P., Le Squeren, A.M., Foy, F., 1988, {\it A\&A}, {\bf 206}, 285

Swope, H.H., 1932, {\it Harvard Obs. Bull.}, No.\,887

te Lintel Hekkert, P., Caswell, J.L., Habing, H.J., Haynes, R.F., Norris, R.P.,
1991, {\it A\&AS}, {\bf 90}, 327

Turnshek, D.E., Turnshek, D.A., Craine, E.R., Boeshaar, P.C., 1985,
An Atlas of Digital Spectra of Cool Stars, Tucson: Western Research 
Company 

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