O. C. Wilson

FLUX MEASUREMENTS OF CA II AND K EMISSION.

A four-channel photon-counting spectrophotometer (designated HKP-2) is described which is designed for measuring stellar chromospheric calcium emission. The HKP-2 is calibrated, and its performance and accuracy evaluated, by observing 63 of Wilsons (1968) program stars on the same nights with both the HKP-2 and a coude scanner designated HKP-1. The results of the observations are discussed in terms of the calibration of mean H-K flux indices, variations in individual stellar fluxes, the flux ratio for H and K, and the instrument color index. It is shown that the HKP-2 provides satisfactory performance in the measurement of stellar chromospheric emission in a manner closely analogous to the method of Wilson and that a single observation yields a color index as well as flux indices for H and K that can be calibrated and transferred unambiguously to Wilsons system of measurement.

Absolute magnitudes of stars from widths of chromospheric Ca II emission lines

The color-magnitude diagram constructed from the M/subv/(K) has several interesting features which are discussed in the text. In particular, the C-M diagram of NGC 188 by Sandage forms an excellent lower boundary to the assemblage of field stars. (AIP)

Recognition and classification of strong-CN giants

Fifty of the stars designated as super-metal-rich by Spinrad and Taylor (1969) are classified here on the Revised MK System. Positive CN indices are assigned in recognition of the characteristic excesses of carbon and nitrogen in their atmospheres, as compared to normal Population I stars. For only a few of the stars, an abnormal strength of the iron lines or of Ca 4226 A is so noticeable that they need to be distinguished by positive indices for these metals.

THE DISTRIBUTION OF INTENSITIES OF BRIGHT H AND K IN DK STARS AND THE RATE OF STAR PRODUCTION IN THE GALAXY

It has recently been demonstrated that the past history of any main sequence star must largely determine, in some manner, the intensity of the bright H and K components in its spectrum. In fact, the most probable interpretation of the observations is that in such an object the H-K intensity, and hence, presumably, the degree of chromospheric activity, is a decreasing function of age. Only in close, short-period, binary systems is there evidence for serious violation of the generally established rule. While there is very probably some intrinsic scatter about any intensity-age correlation, the observations indicate that it is not large, at least for the majority of the stars.1

INTERNAL MOTIONS IN THE PLANETARY NEBULA IC 4997

The small, bright planetary nebula IC 4997 has become of interest in recent years because of its high density1 and because of secular changes in the relative intensities of the [O in] λ 4363 and Ηγ λ 4340 lines.2 Moreover, it has been reported3 that the form of the [Ne ni] line at λ 3869 is such that it requires a fairly rapid rotation of the nebula for its interpretation. The idea of nebular rotation, which originated with Campbell and Moore,4 is, however, difficult to support because of angular momentum considerations. Also, one of us (O. C. W.) has shown that tilted nebular lines can be accounted for simply by a combination of nonuniform ejection velocities within the nebula, together with nonperpendicularity of the line of sight to the major axis.5 These considerations led us to observe IC 4997 with the 32-