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Digital reduction of speckle interferometry data for the K2 III giant a Boo (Arcturus) has been done. Angular diameters of o': 019 i 0': 006 were obtained at 4200 A for a uniformly illuminated disk, and 0,027 i 0,010 for a highly limb-darkened disk. Arcturus is underresolved using the Kitt Peak National Observatory 4-meter telescope. The digital-reduction scheme described here proved ideal for studying such underresolved objects. A discussion of limitations of this technique is also provided. Key words: speckle interferometry - atmospheric seeing - resolution

Evidence for periodic radial velocity variation in Arcturus based on Doppler accelerometer studies is reported. The most likely period and amplitude for these variations are 1.842 + or - 0.005 days and 160 + or - 10 m/s, respectively. Epoch-folding of 31 nights of Arcturus data taken between December 21, 1985 and March 31, 1986 reveals a sawtooth phase diagram. Two physical mechanisms as potential causes of this variation are briefly discussed.

Sensitive X-ray observations have been obtained of alpha Boo and alpha CMi using rocket-borne large area proportional counters. No flux was detected from either star, yielding limits on intrinsic luminosity in the 75-2000 eV band (6-165 A) as stringent as 10 to the 28-th power ergs per sec depending upon assumed coronal temperature. These are at least an order of magnitude better limits than previously reported values. Upper limits are also set on a mass loss rate of three billionths solar mass per year and on an emission measure of less than 3 times 10 to the 53-rd power per cu cm. If these stars are typical, then giants and subgiants cannot be responsible for a significant fraction of the soft component of the diffuse X-ray background.

_____ _____ _____ ____ _____ _____ _____ ____ _____ _____ __ :HERCULES AU IA.e u /RS GEMINIj CELESTIAL TIME TABLE OPHIUCHUS Castor ZAt 0 May 3 1:44 a.m. EDT Moon in last quarter l MAJOR . Pollux n 5 6:00 a.m. Moon farthest, distance 251,600 w BOOTES CANIS MINOR miles Arcturus LEOyo 11 3:05 a.m. New Moon; partial eclipse of |ERPENS Procyon sun visible in Europe and Regulus Arctic regions VIRG 12 9:00 p.m. Moon passes south of Mercury 14 2:00 p.m. Moon passes south of Venus LlB.RA\,Ia 15 8:00 a.m. Moon passes south of Saturn 16 8:00 p.m. Mercury farthest east of sun; CORVUS visible around this date low in west soon after sunset 18 6:29 a.m. Moon in first quarter 20 4:00 p.m. Moon nearest, distance 228,900 SOUTH miles 23 9:00 p.m. Venus passes north of Saturn * * 25 1:51 a.m. Full moon; total eclipse of Stars in Order of Brightness moon, visible generally in When held above viewer and compassNorth and South America oriented the center of the chart is overhead

A detailed non-LTE study of the CN(0,0) 3883 A band-head spectrum of Arcturus (K2 III) provides an accurate determination of the carbon, nitrogen, and oxygen abundances in Arcturus. Non-LTE effects are significant, and we find that the Ayres-Linsky model provides adequate fit to the observations for C,N/sub*]/=1/ 3C,N/sub sun/ and O/sub*]/=0.60)(O/sub sun/, or for C,N,O/sub*]/ =1/6C,N,O/sub sun/, but the latter abundances are unlikely. The upper photospheric microturbuluence is found to be 2.5 +- 0.2 km s$sup -1$. (AIP)

A more extensive and detailed non-LTE simulation of the Delta v = 1 bands of CO than attempted previously is reported. The equations of statistical equilibrium are formulated for a model molecule containing 10 bound vibrational levels, each split into 121 rotational substates and connected by more than 1000 radiative transitions. Solutions are obtained for self-consistent populations and radiation fields by iterative application of the 'Lambda-operator' to an initial LTE distribution. The formalism is used to illustrate models of the sun and Arcturus. For the sun, negligible departures from LTE are found in either a theoretical radiative-equilibrium photosphere with outwardly falling temperatures in its highest layers or in a semiempirical hot chromosphere that reproduces the spatially averaged emission cores of Ca II H and K. The simulations demonstrate that the puzzling 'cool cores' of the CO Delta V = 1 bands observed in limb spectra of the sun and in flux spectra of Arcturus cannot be explained simply by non-LTE scattering effects.

The ultraviolet and near-infrared spectra of O I in Arcturus are analyzed by a 15-level 14-transition model for O I and the Ayres-Linsky (1975) model chromosphere. It is found that the anomalously bright O I resonance lines at 1302, 1305, and 1306 A can be readily explained by a Ly-beta-pumped fluorescence mechanism as originally proposed by Bowen (1974). Observed equivalent widths of the near-infrared triplet and singlet lines are also consistent with the model predictions, but the intercombination lines at 1355 and 1359 A and near-infrared quintet lines may pose a problem.

IUE far-UV and Einstein Observatory soft X-ray observations for the red giant Arcturus and the nearby yellow dwarf Alpha-Centauri A, which are archetypes of solar mass stars in different stages of evolution, are compared. Evidence is found for neither coronal soft X-ray emission from the red giant, at surface flux levels of only 0.0006 that detected previously for the yellow dwarf, nor C II and IV resonance line emission at surface flux levels of only 0.02 those of the yellow dwarf. The resonance line upper limits and previous detections of the C II intersystem UV multiplet 0.01 near 2325 A provide evidence for an Arcturus outer atmosphere that is geometrically extended, tenuous and cool. The red giant has, in addition, a prominent cool stellar wind. An extensive tabulation of line identifications, widths and fluxes for the IUE far-UV echelle spectra of the two stars is given, and two competing explanations for the Wilson-Bappu effect are discussed.

We investigate the generation of extended chromospheres and mass loss of late-type giant stars due to acoustic shock waves. Effects of both monochromatic waves and acoustic frequency spectra are studied. For our wave computations we use an eulerian time-dependent hydrodynamic code based on the method of characteristics. The possible boundary conditions for the cases of suband supersonic inand outflows are discussed in detail. Ionization of hydrogen is explicitly taken into account. Radiation damping is considered in the thin plasma approximation using a Cox and Tucker type law, fitted on the emission function as given by McWhirter, Thonemann, and Wilson (1975). We obtain three different types of stellar wind solutions: Short-period, acoustic-wave calculations show that a persistent wave energy flux can produce an extended chromosphere. If monochromatic shock waves are used no appreciable mass loss is generated. However, in the case of wave models with stochastically changing wave periods episodic mass loss occurs. This behavior is caused by overtaking and merging of shocks. Occasionally very strong shocks are produced. But the time-averaged mass-loss rates related to these stochastic wave models remain very small. The third type of stellar wind solutions is the generation of continuous mass loss in adiabatic wave models with large wave periods. For these models the wavelengths must be comparable to or larger than a stellar radius. In the case of Arcturus, a mass-loss rate between 10~10 and ΚΓ11 3KO y"1 is found. The final flow speed of the wind is larger than 40 km s1. We have applied our method to individual stars, which are: Arcturus (a Bootis), Aldebaran (a Tauri), and Betelgeuse (α Orionis). The chromospheric extents which we find in our time-dependent wave models are 1.12 r*, 1.13 r*, and 1.22 r*, respectively, corresponding to a time-averaged electron density of 107 cm3. These extents are significantly smaller than those derived by Stencel (1981) and Carpenter, Brown, and Stencel (1985), but in the case of Arcturus and Aldebaran, they confirm the results of Judge (1986a, b). The chromospheric temperatures in our wave models increase with height, starting from 6000 Κ up to about 15,000 Κ at the temperature maximum.

In four-color, intermediate-band photometry of late-type stars, difficulty has been experienced in reproducing the Str5mgren system as defined by standard stars published by Crawford and Barnes. The difficulty is believed to be connected with the fact that an international, bulk order for filters has produced a considerably narrower V filter than that used in the original observations of the standard stars. Because of this difficulty a new system has been defined which is characterized by (b - y) = (b - y) Str6mgren, M1 = m1 (Str5mgren) for (b-y) < and C1 (Str6mgren) for (b-y) < 020. The use of M1 as a metal-abundance parameter is demonstrated with Hyades-cluster and group stars and members of the Arcturus group, as well as with some very metal-weak subdwarfs. Key words: uvhyP photometric system - photometric calibrations - standard stars

Possible wind models for late-type stars which appear not to have hot coronae and transition regions are investigated; taking Arcturus and the prototypical star, models with T less than approximately 20,000 K are considered, and solutions with mass loss rates of 10 to the -9th solar masses per year are sought. The radiation pressure of L-alpha resonance scattering can exceed the force of gravity in the chromosphere and initiate a net outflow, but is insufficient to sustain a wind, except perhaps in the presence of an additional momentum input term such as Alfven wave pressure. It is concluded that L-alpha radiation-pressure-initiated winds can occur in stars to the right of the Linsky-Haisch dividing line in the H-R diagram between stars with and without transition regions and presumably hot coronae, and that the existence of these winds may explain energetically the absence of hot coronae in these stars.

We estimate the surface gravity of the K giant Arcturus by comparing synthetic spectra based on model atmospheres with measured wing shapes of the Ca I and Ca II resonance lines calibrated by absolute photometry. Our result, log gapprox. =1.6 +- 0.2 cm s/sup -2/, is consistent with previous spectroscopic estimates based on weak line ionization ratios, with the exception of a recent determination by Maeckle et al. We obtain a stellar mass of 1.1/sub 0//sub .//sub 7//sup 1//sup .//sup 7/ M/sub sun/ for R=27 R/sub sun/. This estimate suggests that Arcturus has not suffered substantial mass loss during its post--main-sequence evolution on the ''ascending red-giant branch.''

Equivalent widths measured from spectrograms obtained with the echelle spectrograph at the Kitt Peak National Observatory are compared in detail with measurements obtained from conventional coude spectrographs. Equivalent width measurements of the bright standard star Arcturus are used to recalculate the composition of that star. The results of all tests performed indicate that equivalent width measurements from the echelle spectrographs are in reasonable agreement with those obtained from other instruments, and can be used reliably to derive element abundances in stars. The degradation of resolution by the image tube should be considered in comparing echelle spectrograms to spectrograms from other instruments with similar reciprocal dispersion; measurements of equivalent widths in crowded spectral regions may be uncertain due to blending.

The paper presents results of high-precision measurements of radial-velocity variations in Alpha Boo. Significant radial-velocity variability is detected well in excess of the random and systematic measurement errors. The radial velocity varies by an amount greater than 200 m/sec with a period of around 2 days.

Precise measurements of the radial velocity of Arcturus were obtained on 43 occasions between 1981 and 1985. The measurements show a 500 m/s range, confirming the radial velocity variability of Arcturus. Multiperiod models which give a good representation of the velocities are derived using a least-squares technique. The models also fit the velocities of Smith et al. (1987). It is suggested that the small-amplitude short-period components of the models could be analogous to the solar five-minute oscillations. The best-fitting models require the largest-amplitude component to have a period of at least 640 days.

Recent laboratory, geophysical, and theoretical determinations of the O I (7990 A) and O I (11,287 A) branching ratios indicate that the generally used values based on the NBS transition parameters need revision. The O I (7990 A) branching ratio is about 300 times smaller than the NBS value, and the O I (11,287 A) is about one-quarter as large. The transitions are important in the generation of permitted atomic oxygen spectra in several types of astronomical source, including the Orion Nebula (M42), the Seyfert galaxy NGC 4151, Arcturus, and comets. The absence of the O I (7990 A) emission in M42 and NGC 4151 is consistent with its very small branching ratio, and previous conclusions based on its absence, such as the rejection of starlight excitation in the Seyfert galaxy, require reinvestigation. The reduction of the O I (11,287 A) branching ratio is pertinent to hydrogen L-beta fluorescence excitation of O I (1304 A) and O I (8446 A) emission and requires an upward revision of oxygen production rates in comets.

High-resolution spectrophotometry of the variable Ca II K line in the K2 IIIp star Alpha Boo was performed with the McMath Solar Telescope at Kitt Peak National Observatory and an experimental SEC vidicon camera. The results are compared with Copernicus observations of the Mg II h and k lines and with earlier Ca II data. It is found that either of two states may typically occur in the Arcturus chromosphere. From comparison with the results of model calculations for expanding chromospheres, it is concluded that these correspond respectively to a 'normal' state in which the mass loss is less than one billionth of a solar mass per year and an 'abnormal' state in which the mass loss is about 8 billionths of a solar mass per year. In the latter case, the expansion velocity is around 13 km/s at optical depth unity in the K-line, which exceeds the local sound speed. It is suggested that the abnormal state represents the rise to the photosphere of a very large convective element, as hypothesized for red giants by Schwarzschild (1975).

Results are reported for a study of the near-UV spectrum of Arcturus as recorded with a balloon-borne echelle spectrograph-vidicon detector system in the spectral region from 2700 to 3300 A at 0.1-A resolution. A condensed version of the Arcturus spectrum is provided along with profile descriptions and identifications for 383 absorption features detected in the near-UV. Elements definitely present include Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, and La. Elements with spectral features indicating possible presence include Be, O, S, K, Ga, Ge, Nb, Sn, Gd, and Bi. Line blocking is shown to be extensive in the spectral region studied, and eight possible continuum 'windows' are found in the near-UV. Emission lines of chromospheric origin due to Mg II, Fe I, Fe II, and possibly Cr II are also identified in the region from 2736 to 3303 A. It is noted that the Fe I emission lines at 2823 and 2844 A are optically pumped.

The formation of the Balmer-series member H-epsilon in the near-red wing of the Ca II H line is discussed for two cases: the sun (H-epsilon absorption profile) and Arcturus (H-epsilon emission profile). It is shown that although the H-epsilon source functions in both stars are dominated by the Balmer-continuum radiation field through photoionizations, the line-formation problems in the two stars are quantitatively different, owing to a substantial difference in the relative importance of the stellar chromosphere temperature inversion as compared with the stellar photosphere.

Spectral line asymmetries have been measured in photospheric lines of Arcturus and the Sun. The asymmetries are not detectable in weak lines but increse with line strength to 3% of the continuum for Arcturus and 5% of the continuum for the Sun. The direction of the asymmetry for Arcturus is opposite that for the Sun, with the line cores shifted toward shorter wavelengths for Arcturus and longer wavelengths for the Sun. Possible explanations of the asymmetries includ granulation motions and acoustic waves.

Models are constructed for the upper photosphere and chromosphere of Arcturus based on the H, K, and IR triplet lines of Ca II and the h and k lines of Mg II. The chromosphere model is derived from complete redistribution solutions for a five-level Ca II ion and a two-level Mg II ion. A photospheric model is derived from the Ca II wings using first the 'traditional' complete-redistribution limit and then the more realistic partial-redistribution approximation. The temperature and mass column densities for the temperature-minimum region and the chromosphere-transition region boundary are computed, and the pressure in the transition region and corona are estimated. It is found that the ratio of minimum temperature to effective temperature is approximately 0.77 for Arcturus, Procyon, and the sun, and that mass tends to increase at the temperature minimum with decreasing gravity. The pressure is found to be about 1 percent of the solar value, and the surface brightness of the Arcturus transition region and coronal spectrum is estimated to be much less than for the sun. The partial-redistribution calculation for the Ca II K line indicates that the emission width is at least partially determined by damping rather than Doppler broadening, suggesting a reexamination of previous explanations for the Wilson-Bappu effect.

The five K giants and one K supergiant included in a precise (HF) radial velocity program all show significant long-term (about 1 yr), low-amplitude (30-300 m/s rms) radial velocity variations which make them unsuitable as precise radial velocity standars. Arcturus has been discussed in detail elsewhere, and the supergiant Epsilon Peg is probably a semiregular variable. The sampling in the five years of data is inadequate to say whether the giants are related to the Cepheid or Mira variables or form an independent class. The amplitudes of the long-term radial velocity variations of the giants and supergiant are correlated with the level of chromospheric activity shown by K line emission intensity and its fluctuation as seen in He I 10830-A. 19 refs.

The ultraviolet spectrum of Arcturus has been observed at high resolution with the IUE satellite. Line identifications, mean absolute 'continuum' flux measurements, integrated absolute emission-line fluxes, and measurements of selected absorption line strengths are presented for the 2250-2930 A region. In the 1150-2000 A region, identifications are given primarily on the basis of low-resolution spectra. Chromospheric emission lines have been identified with low-excitation species including H I, C I, C II, O I, Mg I, Mg II, Al II, Si I, Si II, S I, and Fe II; there is no evidence for lines of C IV, N V, or other species requiring high temperatures. A search for molecular absorption features in the 2500-2930 A interval has led to several tentative identifications, but only OH could be established as definitely present. Iron lines strongly dominate the identifications in the 2250-2930 A region, Fe II accounting for about 86 percent of the emission features and Fe I for 43 percent of the identified absorption features.

IPCS spectra centered on 6200 A at 6.7 A dispersion have been obtained for four giant stars 47 Tuc-L5427, M71-AH78, M71-AH77, and Arcturus. An abundance analysis relative to Arcturus gives values of [Fe/H] = -0.4 and -0.75 for M71 and 47 Tuc, respectively, and near solar-like ratios of Ti, V, and Zr relative to Fe. Reanalysis of the coolest star AH77 with a higher temperature and lowered continuum gives an Fe abundance and Ti/Fe ratio reminiscent of some recent echelle-derived abundance analyses.

Faint, diffuse emissions near 1380 A in deeply exposed IUE spectrograms of the red giant Arcturus very likely are associated with bands of the A-X fourth-positive system of carbon monoxide, fluoresced by multiplet UV2 of neutral oxygen near 1305 A. Numerical simulations indicate that the strength of the CO bands is exceedingly sensitive, in the best available one-dimensional model of the chromosphere of Arcturus, to a delicate balance between the rapid inward attenuation of the oxygen radiation field and the rapid outward decline of the molecular absorptivity. The fortuitous character of the overlap region in the single-component model argues that one should also consider the possibility that the pumping occurs in a highly inhomogeneous chromosphere, of the type proposed in previous studies of Arcturus based on observations of the infrared absorption bands of CO.

Evidence is presented that many of the weak features observed with International Ultraviolet Explorer (IUE) in the far-ultraviolet (1150-2000 A) spectrum of the archetype red giant Arcturus (K2 III) are A-X fourth positive bands of carbon monoxide excited by chromospheric emissions of O I, C I, and H I. The appearance of fluorescent CO bands near the wavelength of commonly used indicators of high-temperature (T greater than 20,000 K) plasma, such as C II at wavelength 1335 and C IV at wavelength 1548, introduces a serious ambiguity in diagnosing the presence of hot material in the outer atmospheres of the cool giants by means of low-dispersion IUE spectra.

Model atmospheres for the K2 III star Arcturus (alpha Boo), calculated with various representations of the atomic and molecular opacity, are compared with the observed flux distribution and a published semiempirical temperature structure. A model computed with the opacity-sampling method and with an effective temperature of 4250 K and a surface gravity of 50 cm/sec per sec matches well, while models with other representations of the opacity produce distinctly worse fits. The effective temperature is well determined at 4250 + or - 100 K.

A statistical description of line blanketing is presented for Arcturus (a Boo, K2 IlIp, V = +0.06) which is based on equivalent widths and identifications of roughly 10,000 spectral lines within the wavelength region AA3600-25,000 A. Equivalent-width contributions or blanketing coefficients for lines grouped as to equivalent width and identification are given for 100 A wavelength intervals for A 9000 A (Tables I and II). Strong lines are listed individually (Table III), and the variation or scatter of blanketing within intervals is described. Corrections to this description for limitations in the observations and their analysis are discussed. Key words: line blanketing - statistics of spectral lines - spectroscopy

WHILST walking on Sunday night with a friend, about 10.35 my attention was directed to a beautiful meteor, of a ruddy hue, not unlike Mars. It appeared a little to the south of Arcturus, and after passing along with a slow motion in an easterly direction, throwing out sparks meanwhile, disappeared near β Herculis. In size it seemed to be about four times as large as Jupiter, and continued visible for three or four seconds. About half a minute afterwards it was followed by another from the same quarter, which took almost exactly the same direction as the other. In colour and appearance it resembled the first, but was not quite so large. It remained visible about three seconds. The sky at the time was beautifully clear, and there was little or no wind.

The domain in the (U, V) plane of old-disk-population stars is defined by a sample of F- and G4ype stars brighter than visual magnitude 6.5 for which luminosities are available from intermediate-band photometry. The majority of these old-disk stars avoid the domain of the young-disk population in the (U, V) plane except for (1) several objects with V near - 17 km sec-1 and (2) a half dozen possible members of a solar group. The sample of stars used to define the old-disk population is confined to distances less than 100 parsecs from the sun and those with V near - 17 km sec-1 may represent several generations of the objects formed in what is now the solar neighborhood and which keep returning to this neighborhood because they are isoperiodic (V near - 17 km sec-1) with the local standard of rest. The half dozen possible members of a solar group indicate an evolutionary age of some 5 X 10 years. In addition to some of the previously recognized stellar groups in the old-disk population (e.g. Wolf 630 and Her), a new group with U = + 40 to + 50 km sec-1 and V = - 36 km sec-1 is also discussed. The sample of red giants: (VE and (R- I)o > + 0"'42) contains eight probable members of the halo population of which five are members of the Arcturus group. Possible structure in the old-disk-population giant sequence is discussed on the basis of published narrow-band indices, and the luminosity functions of the old-and the youngdisk-population red giants are compared. Key words: old-disk population - space motions - red-giant stars

THE “two remarkable meteors” closely following each other, observed by Mr. Hope on May 13 (NATURE, vol. xvi. p. 43), proceeded most probably from a shower in the small southern constellation Crater. Your correspondent describes the point of first appearance as a little south of Arcturus. If this means about 7° or 8° below that star, then the observed courses accord well with the centre indicated, which is apparently quite a new radiant. From the Italian catalogue of 7,512 meteor paths (observed by Schiaparelli, Denza, and others in 1872) which I have lately been reducing, I found this shower at R.A. 170°, Dec. 10° S. (near e—θ Crateris) for May 3–15 from nine meteors.

Star Arcturus chromospheric Lyman alpha emission observation by rocket-borne precision pointing telescope and UV spectrometer