Color magnitude diagram

Photometric methods are widely used to determine overall metallicity, and measure the blanketing in either broad or narrow bands due primarily to Fe and Fe-peak blends, or common molecular features, such as CN. These measures can be calibrated to a true [Fe/H] or can be interpreted through analysis of color-magnitude diagrams with the help of theoretical isochrones through their... 

Fig. 1. The color-magnitude diagram of NGC 188 from [2] with the location of the detached eclipsing binary V12 [3] overplotted. From radial-velocity measurements we find (assuming an inclination of 90 degrees since we do not yet have photometry of the eclipses) that the masses of the two components are 1.06 and 1.08 solar masses. We estimate that we will be able to reach a precision of 1% in the mass estimate. We are in the process of acquiring eclipse photometry such that the radii and orbital inclination can be determined. Since both components are very close to the cluster turnoff their masses and radii can be directly used to give a very accurate age estimate for the cluster by comparing to isochrones in the (mass, radius) plane and requiring that they both lie on the same isochrone.

Abstract. We use intermediate resolution (II, 19 300) spectroscopic observations in the spectral region including the Li 6708 A line to study 341 stars in the star forming region (SFR) NGC 6530. Based on the optical color-magnitude diagrams (CMD), they are G, K and early M type pre-main sequence (PMS) cluster candidates. 72% of them are probable cluster members since are X-ray sources detected in a Chandra-ACIS observation ([2]). We use our spectroscopic measurements to confirm cluster membership by means of radial velocities and to investigate the Li abundance of cluster members. 

Fig. 1. Various color-magnitude diagrams for NGC 1851 obtained with uvby filters at the Danish 1.54m telescope on La Silla. Seven stars in our sample have previous low-resolution spectroscopy from [2] which classified them into CN strong (open squares) and CN normal (plusses) groups. Note how the CN strong stars stand out clearly from the cluster sequences when using filter combinations involving the u and v filters. We see from the lower righthand panel that the RGB stars in this cluster also show a large scatter in the mi index at a fixed luminosity - this is the only cluster in our sample of 20 which show mi scatter. This points to very large C variations (larger than for other clusters). Could this be related to the bimodality of the cluster horizontal branch ...

We have deep color-magnitude diagrams in 4 fields situated at 3, 5, 6 and 8 degrees from the LMC bar (see [3]), in which we are performing CaT follow-up spectroscopy with HYDRA at the CTIO 4m telescope. As it is discussed in [3], the age of the population is older when we move away from the bar. At the moment we have low-resolution spectroscopy for the fields situated at 5 and 8 degrees. The histogram of the metallicities for each field is shown in fig. lb. 

Abstract. We have studied the effects of an hypothetical initial generation made only of very massive stars (M > 100M , pair-creation SNe) on the chemical and photometric evolution of spheroidal systems. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results produced are at variance with the main observational constraints of ellipticals such as the average [< a/Fe > ] ratio in stars and the color-magnitude diagram. 

Figure 3.3. Left color magnitude diagram for the Coma cluster (Savine 2002). The red sequence is well visible with its horizontal pattern. Right color magnitude diagram for the CIG J0848+4453 z=1.27 cluster (Van Dokkum et al. 2001).

Color-magnitude diagrams of galaxy populations can provide some information on the metallicity (or metallicity spread) of a stellar population, since features in the CMD, such as the color of the red giant branch, can vary with metallicity. Unfortunately these features also vary with age of the populations, so there is a degeneracy between age and metallicity in the CMD (and in composite colors). Systematic uncertainties may... 

Ursa Minor appears to have something like a simple, monometallic stellar populations based on its color-magnitude diagram (Mighell Burke 1999, but see below). 

Abstract. Pidiminaiy analysis is presented for J, H, and K images of the Corona Australis doud core. Color-color and color-magnitude diagrams reveal rdatively few new duster members. We condude that the R Cr A infrared duster consuts of only about 30 members and its size reflects the available reservoir of molecular gas. 

Fig. 1. The R-K vs. K color magnitude diagram of the galaades for whidi redshifts were obtained, dotted lines show the trajectory of a brightest duster galaxy. The ledshifi distribution of the galaxies with measured redshifts. The median redshift is >0.5. Sndi a high median redshift requires a modest brightening of galaxies at high redshift.

Key wordsi globular dusters - IR photometry - color-magnitude diagrams... 

J and K photometry for each cluster was obtained using DAOPHOT. The K, J—K color-magnitude diagram (CMD) for Terzan 5 is presented in Fig. 1 as an example. 

Figure 1 is a color-magnitude diagram of all detected point-source objects from these fields. The curve r resents model VLM stars and brown dwarfs om Burrows 1992 (a Y=0.28 version of the Burrows et al. 1993 models.) The brown dwarf/star transition occurs at approximately 0.075 M0. The effective temperature along the Y-axis is simply a blackbody estimate of temperature based on the I-E or J-K color. 

During two runs we have secured high quality J and K images for a sample of about 15 GGC with different metallidties. Here we present preliminary results for 6 GGC M 30, M 15, M 4, M, 68, M 69, NGC 6553. Their Color Magnitude Diagrams (CMD) are plotted in Figure 1 more than 9000 stars were identified in total (though in M4 and M 68 only one fidd has been reduced so far). 

Fig. 1. Comparison of the observed Kvs.J — K color magnitude diagram for the program stars (iiUed boxes) and the unbiased sample of Baade s Window M giants (solid and di ed lines) from Frogel Whitford (1987).

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