5 Clusters projected on the disk

Metal-rich globular clusters projected on the disk are particularly important because they may provide clues to a connection between the globular cluster system and the open cluster system. We note that recently another globular cluster projected on the disk, NGC6749 ($l=36.2\mbox{$^{\circ}$}$,$b=-2.2\mbox{$^{\circ}$}$), was studied by means of V, (V-I) CMDs (Rosino et al. 1997; Kaisler et al. 1997). However, differently of the three cases discussed in the present paper, it is metal-poor and must be related to the halo family.

The spectra of the present sample of clusters projected on the disk are discussed in what follows, three of them are reinstated as probable globular clusters and two are open clusters.

5.1 BH176

This object, located at Galactic coordinates $l=-31.6\mbox{$^{\circ}$}$, $b=+4.3\mbox{$^{\circ}$}$, has been studied by Ortolani et al. (1995b) in terms of ($V,\ I$) CMDs, finding GB and HB morphologies of a metal-rich globular cluster. They derive E(B-V)=0.77 and a metallicity $[M/H]\approx-0.4$.

The present spectroscopic reddening is somewhat lower but consistent with their value. The metallicity (Table 3) confirms that BH176 is a metal-rich cluster. The cluster structure is similar to that of a loose globular cluster (see Fig. 1 in Ortolani et al. 1995b, and ESO/SERC Sky Survey field224), but the number of stars would be unusually large for an open cluster.

5.2 Lyngå7

This cluster at $l=-31.2\mbox{$^{\circ}$}$, $b=-2.8\mbox{$^{\circ}$}$ was suggested to be a globular cluster by Ortolani et al. (1993b) using ($V,\ I$) CMDs. They found E(B-V)=0.72 and $[M/H]\approx-0.4$,and detected GB and HB morphologies compatible to those of a metal-rich globular cluster, and also measured a value for the magnitude difference between the HB and the turnoff ($\Delta^{\rm TO}_{\rm HB}=3.1$) comparable to those of young globular clusters like Ruprecht106, Palomar12, Arp2, IC4449 and Terzan7 (Chaboyer et al. 1996). Lyngå7 was reinstated as a likely globular cluster by Tavarez & Friel (1995) by means of spectroscopy of individual giants and from location, kinematics and metallicity arguments; they obtained E(B-V)=0.73 and $\hbox{$.\!\!^{\rm h}$}=-0.62$.

The present integrated spectroscopy (Table 3) confirms the previous reddening estimates and also indicates the cluster as metal-rich. The cluster structure is similar to that of a loose globular cluster (see Fig. 1 in Ortolani et al. 1993b, and ESO/SERC Sky Survey field178), but likewise BH176, it would be unusually populous for an open cluster.

5.3 Palomar10

This cluster at $l=52.4\mbox{$^{\circ}$}$, $b=+2.7\mbox{$^{\circ}$}$ was recently studied in V, (V-I) CMDs by Kaisler et al. (1997), showing that the RGB and HB morphologies are those of a metal-rich globular cluster. They derived E(B-V)=1.66 and estimated $\hbox{$.\!\!^{\rm h}$}=-0.1$,and a concentration parameter c=0.58, thus a loose cluster.

The present spectroscopic reddening and metallicity (Table 3) basically confirm their values.

5.4 Open clusters

5.4.1 UKS2

This cluster is located at $l=-84.0\mbox{$^{\circ}$}$, $b=-3.0\mbox{$^{\circ}$}$ and was included in the integrated infrared photometry by Malkan (1982) who obtained a reddening of E(B-V)=0.7. ZW84 based on the same data estimated $\hbox{$.\!\!^{\rm h}$}=-0.29$. Armandroff (1988) presented images of UKS2 and suggested that it was an open cluster.

The integrated spectrum (Fig. 11) has strong Balmer lines typical of $t\approx1$Gyr clusters, as shown by the appropriate template match I1, and the continuum distribution indicates that UKS2 is affected by E(B-V)=0.20 (Fig. 11, top panel). Since this is a rather loose cluster in a crowded disk field, contamination might be important, so it would be worth obtaining a CMD to check the derived reddening and age.

  

Figure 11: Bottom panel: observed spectrum of UKS2; top panel: reddening corrected spectrum of UKS2 compared to the I1 template ($t\approx1$Gyr). Main absorption features are labelled. Units as in Fig. 1

Since the integrated near-infrared light is essentially not affected by dilution effects of brighter turnoffs for young clusters, the CaII triplet is a good metallicity indicator for intermediate age clusters, by adopting a globular cluster calibration (BA87). The metallicity obtained for this 1Gyr cluster ($\mbox{$[Z/Z_{\odot}]$}=-0.15$) is consistent with that derived by ZW84.

5.4.2 ESO93-SC08

A CMD of this object, at $l=-66.5\mbox{$^{\circ}$}$, $b=-4.0\mbox{$^{\circ}$}$, indicates that one is dealing with an old open cluster with age $\approx4$Gyr (Bica et al. 1998).

In Fig. 12 we show the observed spectrum (bottom panel) and the reddening-corrected one (E(B-V)=0.35) compared to the intermediate age template I2 (2 - 3Gyr) and the metal-rich globular cluster template G2. From the continuum distribution, both lead to the same reddening value. Using the same arguments for an intermediate age cluster as discussed for UKS2 above, we conclude that ESO93-SC08 is metal-rich from the CaII triplet ($\mbox{$[Z/Z_{\odot}]$}=-0.34$, Table 3). With respect to age, notice that the Balmer lines are particularly strong for this cluster, but not as much as in the 1Gyr template (I1). On the other hand, such Balmer enhancement is not observed in metal-rich globular clusters, such as the G2 template. We conclude that the integrated spectrum of ESO93-SC08 is consistent with that of an old open cluster.

  

Figure 12: Bottom panel: observed spectrum of ESO93-SC08; top panel: reddening corrected spectrum of ESO93-SC08 compared to the I2 template ($t\approx$ 2 - 3 Gyr), and the metal-rich globular cluster template G2 ($\mbox{$[Z/Z_{\odot}]$}=-0.5$). Main absorption features are labelled. Units as in Fig. 1