The Astrophysical Journal, 209:489-496, 1976 October 15 © 1976
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O'! 00^r1 o CN The Astrophysical Journal, 209:489-496, 1976 October 15 © 1976. The American Astronomical Society. All rights reserved. Printed in U.S.À. ft uo r- THE BEHAVIOR OF THE Mg n DOUBLET FEATURES NEAR 2800 A OBSERVED IN F, A, AND B SUPERGIANTS Y. Kondo* NASA Johnson Space Center, Houston, Texas AND T. H. Morgan! and J- L. Modisette Houston Baptist University, Houston, Texas Received 1975 December 22; revised 1976 March 22 ABSTRACT The Mg ii doublet features near 2800  were recently observed in F-, A-, and B-type super- giants with a balloon-borne ultraviolet stellar spectrometer. The stars observed are a UMi (F8 lb), a Per (F5 Ib), rj Leo (A0 lb), and p Leo (B1 lb). The Mg n doublet features in a UMi and a Per show emission superposed upon photospheric absorption. In the spectrum of rj Leo, the Mg ii lines are in absorption and show shortward-shifted components attributable to mass loss. In the spectrum of p Leo, the Mg n lines are primarily a composite of the photospheric and interstellar absorption features. The general behavior of the Mg n lines for supergiants of spectral types M-B are also discussed. Subject headings: stars : emission-line—stars: mass loss — stars: supergiants — ultraviolet: spectra I. INTRODUCTION resolution attained was 0.4  (FWHM). The behavior Emission in the cores of the Mg 11 doublet lines of the Mg ii doublet features in giant and main- (2795.5 and 2802.7 Á) is among the few chromospheric sequence stars has been treated elsewhere. For most diagnostics available for the temperature range rep- recent works, the reader is referred to Kondo, resented by the F stars. High-resolution observations Morgan, and Modisette (1976) and Kondo et al. of the doublet lines are required to detect this emission; (1976). such observations of the doublet lines in main- sequence stars have already been used to establish II. OBSERVATIONS the existence of chromospheres at least to F2 (Kondo et al. 1972). Extension of these observations to F The observations of a Umi, a Per, 77 Leo, and p Leo supergiants is desirable. Accordingly, in the fifth flight are shown in Figures 1, 2, 3, and 4, respectively. of our BUSS (Balloon-borne Ultraviolet Stellar Relatively strong absorption lines in a Per (Fig. 2) Spectrometer) payload, launched from Palestine, have primarily been identified using the line identifica- Texas, on the evening of 1975 March 14, we included tions for a CMi (F5 IV) by van der Hucht et al. (1976). the supergiants a UMi (F8 lb) and a Per (F5 lb) in They are mainly Fd 11 and Cm lines; while neutral the flight-observing plan. We also observed an A-type metal lines are conspicuous in the solar spectrum, the supergiant rj Leo (A0 lb) as a follow-up on the mass lines of once-ionized metals are more prominent in loss observed in the Mg 11 spectrum of a Cyg (A2 la) the spectrum of an F5 star. A similar effort to identify by Kondo, Morgan, and Modisette (19756). For superposing absorption features in a Umi (Fig. 1) comparison, a supergiant of still earlier spectral type using line identifications for a CMi and those for the p Leo (B1 lb) was also included in our program. These Sun (Greve and McKeith 1974) has not yielded four stars were among the 20 successfully observed consistent results. This difficulty is probably due to the during the flight. lower signal-to-noise ratio in a UMi data than in a In this paper the observations are first presented, Per. The dotted lines in Figures 3 and 4 are computed then compared with analogous observations of similar synthetic photospheric lines drawn using the technique systems, and, finally, an interpretation of these results originally developed by Modisette, Nicholas, and is offered. Most aspects of the instrumentation, of the Kondo (1973) and later modified for use on these operation of the payload, and of the data-reduction types of stars by Kondo, Modisette, and Wolf (1975); techniques have been discussed elsewhere (Kondo, the curves are basically Gaussian with several con- Morgan, and Modisette 1975a). The exit slit width straints, and the method is described in detail in the of the spectrometer was 0.25 Â; the ultimate spectral latter article. These four figures show intensity in photon counts per \  interval corrected for back- * Adjunct Professor with the University of Oklahoma and ground, dark count, and relative response; thus they the University of Houston. represent the most basic data. Further, the wavelength t Also Visiting Scientist at NASA Johnson Space Center. scale contains both the heliocentric and radial velocity © American Astronomical Society • Provided by the NASA Astrophysics Data System O'! 00 O'! CMo 490 KONDO, MORGAN, AND MODISETTE ^0 a ALPHA URSAE MINORIS uo r- WAVELENGTH (A) Fig. 1.—Observations of a UMi near 2800  obtained on 1975 March 14-15. Background has been subtracted. Error bars correspond to 1 a. Long arrows indicate line centers, while short arrows indicate limits for Mg n emission features. corrections for each star. We have computed absolute was different, no agreement should be expected in the flux levels for these observations using the results values of the stellar flux corresponding to the unit of the mid-ultraviolet spectrometer on board the (10) photon counts. Apparent similarity in the flux OAO-2 Wisconsin Experiment Package, which in values in Table 1 are merely coincidental. Un- turn was calibrated using on-board calibration devices certainties in these values are attributable to the BUSS and rocket observations (Bless 1975). We have taken and OAO-2 measurements and the conversion pro- two bright stars, a Vir and a Leo, which were com- cedures; the exact magnitude of the errors is difficult mon in the OAO-2 and BUSS (1975 March 14-15) to assess. A very rough estimate of the errors is observations. The brightest stars were chosen in order about 30 percent of the flux values tabulated in Table to minimize the uncertainties due to the background 1. corrections in both results. Among other factors that III. DISCUSSION may have contributed to the uncertainties in the computed absolute flux levels are the possible varia- a) F-type Super giants a UMi and a Per tions in the residual ozone absorption above the Existing high-resolution observations of the Mg ii balloon float altitudes which fluctuated a kilometer or doublet features in F supergiants in the literature are so about the median altitude of 40 km. The optical quite limited. Observations of a Car (F0 lb) obtained efficiency of the telescope detector system and the with the Copernicus V2 spectrometer, which has a extinction were calibrated together. nominal slit width of 0.397  (Rogerson, Spitzer, The computed conversion factors for the absolute et al. 1973) and a resolution of 0.51  (McClintock flux are listed in Table 1. The absolute flux is given in -2 -1 1 et al. 1975), show emission in the (photospheric) terms of ergs cm s “ for 10 photon counts for absorption core of both lines; the emission in turn each star. Since the integration time for each star exhibited a pronounced self-reversal at the center. TABLE 1 The BUSS observations of a UMi, which is an F8 lb object, show the Mg n doublet in emission at the Conversion of Photon Counts to Absolute Flux outside the Earth’s Atmosphere Using Calibrated OAO-2 Results center of absorption features centered at 2795 and 2802 Â. In addition, each emission component exhibits Absolute Flux a weak self-reversal, which may in part be due to Star Photon Counts (ergs cm-2 s-1 À-1) interstellar absorption. Similar self-reversals super- 12 posed on much stronger emission features have been a Umi 10 4.0 x IO" reported for a Ori (M2 lab) by Kondo et al. (1972), a Per* 10 7.5 x 10~12 r? Leo 10 4.7 x lO“12 for e Peg (K2 lb) by Kondo, Morgan, and Modisette P Leo 10 1.2 x 10"11 (1975a), and for a Sco (Ml lb) and a Ori by Bernat and Lambert (1976). In all of these three late-type * To be applied to Fig. 2. supergiants, the emissions were clearly seen against © American Astronomical Society • Provided by the NASA Astrophysics Data System PERSEI ALPHA © American Astronomical Society • Provided by the NASA Astrophysics Data System O'! 00^r1 O'! CMo 492 KONDO, MORGAN, AND MODISETTE Vol. 209 ^0 a ETA LEONIS uo r- Fig. 3.—Observations of 17 Leo near 2800  obtained on 1975 March 14-15. Background has been subtracted. Error bars corre- spond to 1 a. Long arrows indicate line centers for resonance doublet. a flat (and weak) stellar continuum; the 2802 emission originally symmetric 2795.5 emission. Bernat and component is symmetric with a central self-reversal, Lambert (1976) have developed a model involving an while the 2795 component is asymmetric. Modisette, expanding gaseous shell surrounding a Ori and a Nicholas, and Kondo (1973), following a suggestion Sco; the absorption causing the asymmetry in the from Herbig, interpreted this asymmetry as the result 2795 emission is caused by Fe 1 and Mn 1 contained in of Fe i absorption at 2795.01  superposed on the this shell. The Mg 11 emission features in a UMi are RHO LEONIS Fig. 4.—Observations of p Leo near 2800  obtained on 1975 March 14-15. Background has been subtracted. Error bars correspond to 1 a. Long arrows indicate line centers for resonance doublet.