arXiv:astro-ph/0303666v2 28 Apr 2003 [email protected] to Correspondence 1 ouainI itneidctr nthe in indicators . Group distance Local primary old- the II the are Population and trace component particular, stellar est in , sample RR Lyrae galaxies. to in populations and stellar as- different scale, the set distance to tronomical important are stars Variable Introduction 1. edopitrqet to requests offprint Send Held .Maio M. 1 2 3 Abstract. 4 aibesasi h a fteLreMglai lu (LMC) Cloud Magellanic Large the so-called of the bar reconcile to the us in stars variable esr faot6 RLrevral tr ntegoua cl globular the in words. stars Key variable t Lyrae We report RR and 6. 60 , and about of 1049) field of this measure (NGC in 3 variables Fornax candidate clusters 1000 33’ stellar a the of containing study photometric the value 2 NF-Osr.Ato.d oon,vaRnai1 02 Bolog 40127 1, Ranzani via Bologna, di Astron. Osserv. - INAF NF-Osr.Ato.d aoa ioodell’Osservatorio Vicolo Padova, di Astron. Osserv. - INAF NF-Osr.Ato.d rr,VaBaci4,287Merate 23807 46, Bianchi Via Brera, di Astron. Osserv. - INAF NF-Cnr aie aie eecpoNzoaeGalile Spain Nazionale Palma, Telescopio La & de Galilei Cruz Santa Galileo 38700 Centro - INAF .Poretti E. , µ 1 LMC .Baldacci L. , ebifl eiworpooercadsetocpcsuyof study spectroscopic and photometric our review briefly We : aelncCod onx–Vral tr itnescale Distance – stars Variable – Fornax – Clouds Magellanic 18 = 3 .Maio M. : .Rizzi L. , . 51 ± 1 .Clementini G. , .Gratton R. 0 . 8 a.Te epeetpeiiayrslsfrom results preliminary present we Then mag. 085 2 short .Bragaglia A. , × 4 rai h onxdafshria spheroidal dwarf Fornax the in area 34’ and 2 .Taribello E. , long oig epeetterslso u study our of results the present fol- we the lowing, In 1997). par- Catchpole trigonometric & Feast about Cepheid allaxes: to (e.g. 1998a,b) mag al. 18.7 parallax et Fernley (e.g. statistical methods: mag and 18.3 in- about Baade-Wesselink from different the ranges fact, from dicators In modulus Way. long distance Milky the a LMC to for vicinity notwithstanding has its uncertain LMC remained the time to distance The Cloud Magellanic Large The 2. 1 .Greco C. , itnemdl fteLCo the on LMC the of moduli distance 1 .Carretta E. , 1 1 .Gullieuszik M. , efis eeto and detection first he ,312Pdv,Italy Padova, 35122 5, se onx3. Fornax uster 2 .D Fabrizio Di L. , ,P o 565, Box PO o, dnie about identified Italy , a Italy na, htallowed that , RLyrae RR 2 E.V. , 4 , 2 M. Maio et al.: Distance scale and variable stars in LMC and Fornax

Fig. 1. Left panel: V vs B − V color - magnitude diagram of our LMC Field A. Larger symbols mark the variables identified in this area. Right panel: examples of our light curves. of variable stars in the LMC and its im- the V light curves (Jurksic & Kov´acs 1996, pact on the short and long distance scale Kov´acs & Walker 2001) for 29 RRab’s. controversy. All these different estimates are in very We obtained time series photometric good agreement to each other, once differ- data (72 V , 41 B, and 15 I frames) of ences in the adopted metallicity scales are two 13’ × 13’ fields (Field A and B) close properly taken into account and give an av- to the bar of the LMC and derived light erage metal abundance of [Fe/H]=−1.5. curves accurate to 0.02-0.03 mag, for 125 We used the VLT spectroscopic metal- RR Lyrae stars (77 RRab’s, 38 RRc’s, 10 licity determinations and our estimates double-mode pulsators RRd’s), 4 anoma- of the average luminosities of the RR lous Cepheids, 11 classical Cepheids, 11 Lyrae stars and reddening, to derive the eclipsing binaries, and one δ Scuti . luminosity-metallicity relation followed by Figure 1 shows, on the left, the loca- the LMC RR Lyrae stars: tion of the variable stars in the HR diagram of Field A; variables are plotted accord- < V0(RR) >= [0.214(±0.047)] × ([Fe/H]+ ing to their intensity-average magnitudes and colors. On the right, we show the light 1.5)+19.064(±0.017) curves for an RRab, an RRc, an RRd and an eclipsing binary in our sample. (Clementini et al. 2003, Gratton et al. 2003, We also derived metallicities for a to- in preparation). tal number of about 100 of the RR Lyrae Our estimate of the dereddened aver- stars using different methods. We applied age luminosity of the RR Lyrae stars in the ∆S method (Preston 1959) to 6 RRd’s the LMC bar is < V (RR) >0= 19.06 mag (Bragaglia et al. 2001), and a revised ver- (at [Fe/H] = −1.5 dex). This value was sion of this technique to spectra obtained combined with a number of recent inde- with FORS at the VLT in 2001 for 101 pendent estimates for the absolute magni- RR Lyrae stars in our sample. Finally, pho- tude of the RR Lyrae stars (e.g. Gratton et tometric metallicities were estimated from al. 2002, Cacciari et al. 2000) to estimate parameters of the Fourier decomposition of the LMC distance. The distance moduli so M. Maio et al.: Distance scale and variable stars in LMC and Fornax 3

Fig. 2. On the left: Instrumental color-magnitude diagram of chip #7; candidate variables are marked as larger symbols. In the center: image 95” × 95” of the NGC 1049, with candidate variables marked as filled squares. On the right: examples of light curves in Fornax 3, [panels (a) and (b)], and in the field, [panels (c) and (d)]. derived where compared with the most re- Fornax dSph have never been adequately cent and accurate LMC distance determi- surveyed for variability, in spite of clear nations from several other Population I and indications, from their HB morphologies, II distance indicators, reaching 1 σ conver- that they should indeed contain RR Lyrae gence on a distance modulus of µLMC = variables (Buonanno et al. 1998,1999). ± 18.51 0.085 mag, as fully described in Fornax 3, one of the two clusters that Clementini et al. (2003). lie in our Fornax field, is quite metal- poor ([Fe/H=−1.96 ±0.20, Buonanno et al. 3. The spheroidal galaxy 1998) and has a relatively well populated Located about 140 Kpc from the Milky Horizontal Branch (HB) characterized by Way, Fornax is a dwarf spheroidal galaxy a very extended HB blue tail. Buonanno et (dSph) dominated by an intermediate-age al. (1998) identified 66 candidate RR Lyrae stellar population (Stetson et al. 1998, stars in this cluster from their limited HST Saviane et al. 2000). There is also evidence data. for an old stellar component, since the We observed an area of 34’ × 33’ North galaxy contains 5 globular clusters and field to the Fornax dSph center with the Wild population as old and metal-poor as that Field Imager (WFI) of the 2.2 m ESO- in globular clusters (Saviane et al. 2000). MPI telescope, with the larger part of the The field of Fornax dSph has been inves- galaxy in chip #6 and #7 of the WFI tigated for variability by Bersier & Wood mosaic. We obtained time series B and (2002) who surveyed a half square de- V photometry (18 V and 62 B frames). gree covering the central region and found Photometric reductions using the packages about 600 variables (among which 515 RR DAOPHOT/ALLSTAR II (Stetson 1998) Lyrae). However, because of the small tele- and ALLFRAME (Stetson 1994) are in scope size and the mediocre seeing condi- progress. Candidate variables were iden- tions of their observations, RR Lyrae are tified using the package ISIS 2.1 (Alard close to the detection limit of their pho- 2000) that works with the image subtrac- tometry, and their observations did not re- tion method. We detected 335 candidate sult in high quality light curves. GCs of variable stars in chip #6 and 190 candidate 4 M. Maio et al.: Distance scale and variable stars in LMC and Fornax variables in chip #7. The globular cluster Bragaglia, A., Gratton, R.G., Carretta, Fornax 3 falls in chip #6. We selected a E., Clementini, G., Di Fabrizio, L. & box of 95” × 95” centered in the core of Marconi, M. 2001, AJ, 122, 207 Fornax 3 and in this area we find about Buonanno, R., Corsi, C.E., Zinn, R., Fusi 70 candidate variables. Even if decontam- Pecci, F., Hardy, E. & Suntzeff, N.B. 1998, ination from the field variables has not AJ, 501, L33 been made yet, these candidate variables Buonanno, R., Corsi, C.E., Castellani, M., are very likely to belong to the cluster, and Marconi, G., Fusi Pecci, F., Zinn, R. 1999, since most of them fall on the cluster HB, AJ, 118, 1671 they are RR Lyrae stars. This is the first Cacciari, C., Clementini, G., Castelli, F. detection and measure of the variable stars & Melandri, F. 2000, in ASP Conf. Ser. in one of Fornax dSph galaxy globular clus- 203, The Impact of Large Scale Surveys on ter system. Figure 2 shows in the left panel Pulsating Stars Research, ed. L. Szabados the (v, v-b) instrumental color-magnitude & D. Kurtz (San Francisco: ASP), ASP, diagram of Fornax dSph field in chip #6, 176 and in the central panel an image of the Clementini, G., Gratton, R.G., Bragaglia, globular cluster Fornax 3. In both pan- A., Carretta, E., Di Fabrizio, L. & Maio, els the candidate variables are marked by M. 2003, AJ, 125, 1309 filled circles. Finally, the right panel shows Fernley, J., Barnes, T. G., Skillen, I., some preliminary light curves of RR Lyrae Hawley, S. L., Hanley, C. J., Evans, D. stars in Fornax GC3 (panels a and b) and W., Solano, E. & Garrido, R. 1998, A&A, Fornax dSph field (panels c and d). These 330, 515 are DAOPHOT instrumental differential b Fernley, J., Skillen, I., Carney, B. W., light curves and only half of the time se- Cacciari, C. & Janes, K. 1998, MNRAS, ries data has been plotted. Photometric re- 293, L61 ductions are still in progress and we ex- Feast, M. W. & Catchpole, R. M. 1997, pect that the photometric quality of the RR MNRAS, 286, L1 Lyrae light curves (about 0.05-0.06 mag for Gratton, R.G., Bragaglia, A., Carretta, each data points in the DAOPHOT reduc- E., Clementini, G. & Grundahl, F. 2002, tions) will improve to a few hundredths of in ASP Conf. Ser., New Horizons in a magnitude for the magnitude calibrated Globular Clusters Astronomy, G. Piotto, Alard fluxes. We also detected 4 candidate G. Meylan, G. Djorvski & M. Riello (San variables in the scarcely populated cluster Francisco: ASP), in press Fornax 6, an object whose actual nature Gratton, R.G., Bragaglia, A., Clementini, still needs to be investigated. G., Carretta, E., Taribello, E., Di We estimate that the total number of Fabrizio, L. & Maio, M. 2003, AJ, in candidate variable stars in the 8 chips of preparation our WFI field of Fornax galaxy is of about Jurksic, J., & Kov´acs, G. 1996, A&A, 312, 1000 (lower limit), to be compared to the 111 600 found by Bersier & Wood 2002 in an Kov´acs, G., & Walker, A.R., 2001, A&A, area about 1.6 times larger than ours. This 371, 579 should be taken into when extrapolating Preston, G.W., 1959, ApJ, 130, 507 Bersier & Wood results to determine the Saviane, I., Held, E.V. & Bertelli, G. 2000, total census of the variable star population A&A, 355, 56. in Fornax dSphs galaxy. Stetson, P.B. 1994, PASP, 106, 250 Stetson, P.B. 1998,”User’s Manual for References DAOPHOT II” Alard, C. 2000, A&AS, 144, 363 http://www.star.bris.ac.uk/ mbt/daophot Bersier, D. & Wood, P.R. 2002, AJ, 123, Stetson, P.B., Hesser, James E., Smecker- 840 Hane, Tammy A. 1998, PASP, 110, 533