Near-infrared photometry of red giant and horizontal branch stars in M4

Phillips, J. P.; Martinez Roger, C.; Sanchez Magro, C.; Lazaro Vilchez, C.
Bibliographical reference

Astronomy and Astrophysics (ISSN 0004-6361), vol. 161, no. 2, June 1986, p. 257-263.

Advertised on:
6
1986
Number of authors
4
IAC number of authors
3
Citations
9
Refereed citations
9
Description
Near-infrared photometry for the red-giant and horizontal branches in M4, obtained with the InSb detector mounted on the 1.54-m Tenerife Infrared flux collector, are presented. The red giant branch is shown to be displaced from the corresponding trend for M92, confirming earlier work, and implying an intermediate to high cluster metallicity. The horizontal branch intersects the RGB at (V - K)0 = 2.0, and continues to increase an additional two or more magnitudes in K towards the BHB, indicating a log (HB luminosity/solar luminosity) of about 1.60 for E(B - V) = 0.46 mag, a value approximately 0.1 mag larger than previous estimates of selective extinction. Color-color and color-magnitude plots show similar trends to those of field stars in the regime of H(-) opacity dominance, though the entire range of cluster stars are seen to depart from the trend in the B - V, V - K plane due to reduced short-wave opacities, a departure also seen in the V - B, V - K plane.