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Variable stars in the field and in the globular
clusters of Fornax dSph
Greco, C., Clementini, G., Held, E.V., Poretti,
E., Catelan, M., DellArciprete, L.,
Gullieuszik, M., Maio, M., Smith, H.A., Pritzl,
B.J., Rest, A., DeLee, N.
The data
The analysis

• Deep B and V time series photometry of Fornax
  field
• (V about 25-26 mag)
• with the WFI of the 2.2m ESO telescope
• 3 nights, November 2002 61 B 17 V
• 4 nights, November 2004 59 B 16 V
• ? at the 4m CTIO/MOSAIC 55 B 128 V
• 3 nights, November 2003
• 2 nights, October 2004
• Deep B and V time series photometry of Fornax 2,
  3, 4, and 5
• (V about 24-26 mag)
• ?at the Magellan/Clay telescope with MagIC
• 3 nights, November 2003, and 2 half
  nights, December 2004

The data observing and reduction strategies
-study of the RR Lyrae and the Anomalous
Cepheids -search for Dwarf Cepheids and binary
blue stragglers -CMDs
Period search and light curve analysis performed
with GRATIS, Graphical Analyzer of TIme Series
(Di Fabrizio 1999 Clementini et al. 2000)
Total area of Fornax dSph covered by our
observations
Fornax CMDs show the presence of three stellar
populations old, intermediate and young
(Buonanno et al. 1985, Stetson et al. 1998 and
Saviane et al. 2000). For the first time Bersier
Wood (2002) identified about 500 candidate RR
Lyrae stars, on an area of about 0.5 deg2
covering the central region of the galaxy. We
present preliminary results on four of the eight
CCDs of the 2.2m ESO WFI, covering an area of
about 0.16 deg2 in the northern field of Fornax.
They are found to contain a total number of more
than 600 candidate variables, on an area of
about one third that of Bersier Wood
(2002). Chip 6 110 RR Lyrae stars, 11
Anomalous Cepheids, 23 Dwarf Cepheids and 15
binaries Chip 7 84 RR Lyrae stars and 21 Dwarf
Cepheids Chip 5 209 candidate variable stars
among which 84 RR Lyrae and 7 Dwarf Cepheids
Chip 8 163 candidate variable stars among
which 14 Dwarf Cepheids
a
b
Chip 6
Chip 7
Fornax field
CMDs of the Fornax field from four of the eight
chips of 2.2m ESO WFI, namely Chip 6 (which
includes cluster For 3), Chip 7, 5 and 8. Red
and blue circles in panels (a) and (b) RR Lyrae
stars, triangles Dwarf Cepheids, squares
Anomalous Cepheids, cyan circles binary stars.
Magenta circles in panels (c) and (d) are
candidate variables not yet classified in types
Analysis has been completed for the variable
stars in Chip 6. CHIP 6 field variables 72
ab-c RR Lyrae, 10 double-mode RR Lyrae, 9
Anomalous Cepheids, 21 Dwarf Cepheids, 15 binary
systems. CHIP 6 cluster For 3 18 ab-c RR
Lyrae, 10 double-mode RR Lyrae, 2 Anomalous
Cepheids, 2 Dwarf Cepheids. From the field RR
Lyrae stars we estimate ? mean periods
ab,field 0.595 d c,field 0.362 d ?
metallicity of the old population Fe/Hfield
-1.77 from log -0.092 Fe/H - 0.389
(Sandage,1993) ? distance field
21.28 ? 0.10 ? (m M)0 field 20.72 ?
0.10 with M V (RR) 0.50 at Fe/H -1.5
One of the most intriguing property of the
Galactic globular clusters is the Oosterhoff
dicothomy a sharp subdivision into two distinct
types according to the mean periods of their RR
Lyrae stars (OoI 0.55 d, OoII 0.65
d). The RR Lyrae stars in the Fornax field
have properties intermediate between the two
Oosterhoff types. Do the Fornax GCs conform to
the Oosterhoff dicothomy? Mackey Gilmore
(2003) identified candidate RR Lyrae stars in
For 1, 2 , 3 and 5 using HST archive data. They
determined periods by fitting template RR Lyrae
light curves to their data, and found that Fornax
clusters possess mean characteristics
intermediate between the two Oosterhoff groups
defined by the Galactic globular clusters. We
have obtained well sampled light curves for RR
Lyrae stars in For 3 and 5 and have performed the
first variability survey of For 4.
Cluster Fe/H
NcNd/NRR For 4 -1.90
0.60 0.359 0.413 0.373
0.235 For 2 -1.79
- Comparison with Mackey
Gilmore(2003) Cluster Fe/H
NcNd/NRR
NcNd/NRR For 3
-1.96 0.606 0.358 0.413
0.395 0.536 0.532 0.613
0.404 0.38 For 5 -2.20
0.576 0.353 0.36 -
0.47 0.532 0.577
0.374 0.68
Fornax Globular Clusters
Fornax GCs in the Oosterhoff plane
First study of the variable stars in For 4!
CMDs, phased light curves and RR Lyrae
period-amplitude diagrams of For 3, 4 and 5.
The Oosterhoff dichotomy inside For 4?
Arrows show the two peaks in the period
distribution of the ab type RR Lyrae stars in
For 4.
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