Spectroscopic Parallaxes Research Articles

POSSIBLE NEARBY F AND G DWARFS

ABSTRACT Spectroscopic parallaxes have been determined for 205 F and G dwarf stars lying between + 100 < 3 < 300. of 46 stars with spectroscopic parallaxes greater than 0'.'04, 18 are found to have no previously determined trigonometric parallaxes. Two of these stars may be within 15 pc. This suggests that the present knowlodge of the relative populations of these types in the solar vicinity may require further investigation. Key words: spectroscopic parallax - nearby stars

The application of multivariate analysis to parallax solutions. 11.Magnitudes and colors of comparison stars

view Abstract Citations (4) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The application of multivariate analysis to parallax solutions. 11.Magnitudes and colors of comparison stars Kerridge, S. J. ; Upgren, A. R. Abstract The application of principal component analysis to parallax solutions is continued from an earlier study and extended to cover the effects of magnitudes and colors among the comparison stars measured. The influence of these parameters coupled with the eight others describing the geometry of the reference frame studied previously, shows little increase in the variance explained by addition of magnitude and color terms. Although the total variance was increased ouly slightly by the introduction of magnitude and color terms, they signifi- cantly increased the stability of the modeL Spectroscopic parallaxes, available for the comparison stars, allowed a precise parallax for the central star. Introduction of this value further increased the stability of the results. A continuation of the program to include observationally determined error sources appears necessary for any additional increase of the total variance explained. Publication: The Astronomical Journal Pub Date: September 1973 DOI: 10.1086/111466 Bibcode: 1973AJ.....78..632K full text sources ADS |

The (log g, log Teff)-Diagram, a Fundamental HR-Diagram

Spectroscopic and photometric parallaxes are based on the assumption that to each point in the relevant region of (g, Teff, a)-space there corresponds a unique mass. The implications of a breakdown in this assumption are discussed briefly and an alternative approach to problems that traditionally have required spectroscopic or photometric parallaxes is presented. This alternative approach involves the use of the (log g, log Teff)-diagram as an HR-diagram.

On the distances of planetary nebulae.

Reconsidering calibration of statistical distance scales for planetary nebulae leads naturally to examining precision and especially the systematic errors of other methods. Here we present a different calibration strategy based on the precise trigonometric parallaxes for sixteen central stars published by Harris et al. (2007) of USNO, with four improved by Benedict et al. using the Hubble Space Telescope. We tested various other methods against those and each other. The statistical scales tested – Cahn et al. (1992), Zhang (1995), Frew (2008), and Stanghellini et al. (2008) – all show signs of radius dependence (i.e. distance ratio [scale/true] depends on nebular radius). Almost all have overall systematic error; Frew’s mean statistical scale seems free of that and also perhaps a scale of Zhang’s based on brightness temperature. Systematic errors were introduced by choices of data sets for calibration, by methodologies used, and by assumptions made about the nebulae. Some spectroscopic parallaxes published by Ciardullo et al. (1999) seem consistent with the trigonometric ones where the objects overlap in nebular radius. Pottasch’s (1996) earlier spectroscopic parallaxes, on the other hand, underestimate distance consistently by a factor of two, probably because of a calibration difference. ‘Gravity’ distances seem to be overestimated by 40-50 per cent for nearby objects but may be underestimated for distant objects. Angular expansion distances appear to be suitable for calibration after correction for astrophysical effects (e.g. Mellema 2004). In particular the measurements by Hajian and collaborators using the VLA seem to yield fairly accurate distances after correction by Frew. Extinction distances appear to be often unreliable individually though sometimes approximately correct overall. Comparison of the Hipparcos parallaxes (van Leeuwen 2007) for large planetaries with our ‘best estimate’ distances confirms that those parallaxes are overestimated by a factor 2.5, as suggested by Harris et al.’s result for PHL 932. The ultimate goal is an accurate and internally consistent set of distances for planetaries. However, some of our tools and analysis can also be applied in distance scale comparisons utilizing parallaxes and/or distances for other objects as well.

MK SPECTRAL TYPES FOR 185 BRIGHT STARS

A program has been initiated at the Yerkes Observatory to determine more accurately the mean direction of the interstellar magnetic field in the vicinity of the sun by observing the interstellar polarization of bright nearby stars in the direction of the galactic poles and in the galactic plane. Spectroscopic parallaxes are needed for the program stars. Spectrograms have been taken therefore for those stars for which no MK spectral types are given either in the Catalogue of Bright Stars (HofBeit 1964) or the Catalogue of Stellar Spectra Classified in the Morgan-Keenan System (Jaschek, Conde, afnd de Sierra 1964). Since accurate spectral types in the MK system may be useful for other investigations as well, the spectral classifications are published in advance of the extended polarimetrie program. All spectrograms were obtained on Kodak Ila-O plates with the Cassegrain spectrograph and the 110-mm camera on the 82-inch reflector at the McDonald Observatory. The dispersion was about 120 A/mm at Hy. Spectrograms of 54 standard stars of the MK system from the revised list of 1953 were obtained during the same observing period. The standard spectra and the criteria of the Yerkes Atlas of Stellar Spectra (Morgan, Keenan, and Kellman 1943) were used to determine the spectral types. When the line ratios were intermediate between those of two standards, interpolated spectral types were given. No attempt was made to determine luminosity classes for peculiar spectra. Spectra with only slight deviation from standard spectra were labeled (p)- The luminosity of these (p)-stars is assumed to be not much different from ordinary stars of corresponding spectral type. The results of the classification are given in Table I. An asterisk following the HR number refers to a remark on the classification at the end of the table.

Spectroscopic parallaxes of M-type supergiants

M-type supergiants have certain advantages as distance indicators: high luminosity, high discovery probability, and extreme redness such that they can be observed efficiently in the infrared where the interstellar absorption is relatively low. It is known that these stars appear in an advanced stage of the evolution of an O-association, such as h/χPersei, in which the most massive members have moved to the right in the HR diagram. They, therefore, represent population I tracers which are somewhat older than, say, the O-type stars.

A preliminary color-magnitude diagram for late-type stars in the solar neighborhood

Modern photoelectric techniques yield magnitudes and colors of stars with accuracies of the order of a few thousandths and a few hundredths of a magnitude respectively. Hence for star clusters it is possible to derive highly accurate color-magnitude arrays since all of the members of a cluster may be considered to be at the same distance from the observer. It is much more difficult to do this for the nearby stars where all of the objects concerned are at different, and often poorly determined, distances. If one depends upon trigonometric parallaxes, the bulk of the reliable individual values will refer to main sequence stars, and while the mean luminosities of brighter stars are given reasonably well by this method, the scatter introduced into a color-magnitude array by using individual trigonometrically determined luminosities could obscure important features. Somewhat similar objections could be raised against the use of the usual spectroscopic parallaxes which also should be quite good for the main sequence but undoubtedly exhibit appreciable scatter for some, at least, of the brighter stars.

Comet-Tail Structures in Emission Nebulae.

A catalogue is given of a large number of "comet-tail" or "elephant-trunk" structures in several emission nebulae whose distances are known from spectroscopic parallaxes The dimensions of the comet- tail structures and the orientations of their axes with respect to the directions to the 0 stars exciting the nebulae are listed The forms of these structures are in general agreement with the theory of their origin presented by van de llulst, Spitzer, Frieman, Layzer, and others. The observational evidence suggests that in the final stages of development of these structures their tips become larger in diameter than their necks and eventually break off, forming separate droplets Several different observations show that the densities in the bright ionized rims of the comet-tail structures are considerably higher than the mean densities of the emission nebulae to which they belong Finally, the application of these structures to the galactic-structure problems of locating distant 0 stars and of determining the distances of H ii regions is discussed

Comet-tail structures in emission nebulae.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Comet-tail structures in emission nebulae. Osterbrock, Donald E. Abstract A catalogue is given of a large number of "comet-tail" or "elephant-trunk" structures in several emission nebulae whose distances are known from spectroscopic parallaxes. The dimensions of the comet-tail structures and the orlentations of their axes with respect to directions to the 0 stars exciting the nebulae are listed. The statistics of these dimensions show that the forms of these structures are in general agreement with the theory of their origin presented by van de Hulst, Spitzer, Frieman, Layzer, and others. The observational evidence suggests that in the final stages of development their tips become larger in diameter than their necks, and eventually break off, forming separate droplets. Several different observations show that the densities in the bright ionized rims of the comet-tail structures are considerably higher than the densities in the main bodies of the emission nebulae to which they belong. Finally, the application of these structures to the galactic structure problems of locating distant 0 stars and of deter mining the distances of Hii regions is discussed. Mount Wilson and Palomar Observatories, Carnegie Institution of Washington, Calofornia Institute of Technology, Pasadena, Calof. Publication: The Astronomical Journal Pub Date: 1957 DOI: 10.1086/107652 Bibcode: 1957AJ.....62S..28O full text sources ADS |

Luminosity Function and Space Motions of G8-K1 Stars Derived from Spectroscopic Parallaxes.

view Abstract Citations (32) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Luminosity Function and Space Motions of G8-K1 Stars Derived from Spectroscopic Parallaxes. Halliday, Ian Abstract Visual MK classifications and luminosity measures made with the help of an oscilloscopic microphotometer have been determined for 227 stars in the spectral range G8-K1, from spectrograms with a dispersion of 33 A/mm An analysis of the luminosities leads to a relative luminosity function which shows a distinct m inimum in the region of the subgiants Spectroscopic parallaxes and space motions are computed for all the stars. For 24 stars the component of the space motion in the galactic plane is 65 km/sec or more. Publication: The Astrophysical Journal Pub Date: September 1955 DOI: 10.1086/146080 Bibcode: 1955ApJ...122..222H full text sources ADS | data products SIMBAD (222)

Spectral classification through photoelectric photometry in narrow wavelength regions.

view Abstract Citations (4) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral classification through photoelectric photometry in narrow wavelength regions. Strömgren, B. Abstract In continuation of previous investigations on spectral classification through photoelectric photometry with interference filters a method of two dimensional classification of B, A and F stars based on measures of the strength of HP and of the Balmer discontinuity has been developed.1 An index measuring the strength of HP is determined with the help of interference filters with maximum transmission at ~oooA, 486 IA, and 47ooA, respectively, while measures through filters with maxima at 4500A, 4030A, and 3550A yield an index measuring the Balmer discontinuity. Both indices are practically uninfluenced by interstellar reddening. The half-width of the HP filter is 35A, the other filters have half-widths around iooA. Measures were made with a photoelectric photometer attached to the 8~-inch reflector of the McDonald Observatory in November and December, 1951, February and March, 1953, and November, 1953. The method was calibrated by measures of about one hundred stars for which accurate spectral classes and luminosity classes by W. W. Morgan were available. The agreement between the two sets of classifications was very satisfactory. For about seventy F stars, of photoelectric B-V color, indices measured by H. L. Johnson, D. Harris, and by P. Naur at the McDonald Observatory were available. For most of these stars interstellar reddening should be very small so that the accuracy of prediction of intrinsic colors from the measured HP and Balmer indices could be tested. The photometric probable error of a predicted B- V value of one observation is +o.oo6 mag. This corresponds to a probable error +0.02 of a spectral class. The comparison between observed and predicted B- V values indicated that cosmical scatter was small, of the order of +o.oo6 mag. or less. The photometric probable error of one observation of a predicted absolute visual magnitude for an F star was found to be +0.18 mag. Comparison with absolute magnitudes from spectroscopic and trigonometric parallaxes gave no indication of cosmic scatter. For the B stars the predicted absolute visual magnitude depends practically only on the HP index. The photometric probable error of one observation was found to be +0.12 mag. Comparison with spectroscopic absolute magnitudes determined by W. W. Morgan indicated no cosmical scatter. An upper limit only could be determined, viz. +0.2 mag. Photoelectric photometry with interference filters (K line, g discontinuity and cyanogen criteria) of about 250 K stars, carried out by Mr. K. Gyldenka~rne with a io-inch reflector of the Copenhagen Observatory, confirmed the results obtained earlier that two dimensional classification is possible here also. The agreement with classification obtained by W. W. Morgan and by Miss Nancy Roman is satisfact~ry. Comparison with color indices measured by D. Harris indicated that for K giants the intrinsic color can be predicted from the K-line criterion with a probable error of one observation about +0.012 mag. Simultaneous photoelectric photometry with photon counters of three narrow wave-length regions, HP and two comparison regions, defined through slits at the coude' spectrograph focus of the 8~-inch reflector of the McDonald Observatory, have been carried out. The experience gained indicates that it will be feasible and advantageous to develop the classification method in this direction. What is required of the spectrograph is fairly high angular dispersion, so that the wave length regions are sufficiently well- defined even with a slitless arrangement. While the interference filter method used with the 82- inch yields high precision down to about 12 mag., simultaneous measures would extend the range of application to about 14 mag. For equal precision the gain over the photographic method is about 4 magnitudes when the photoelectric accumulation time is equal to the photographic exposure time. Publication: The Astronomical Journal Pub Date: 1954 DOI: 10.1086/107090 Bibcode: 1954AJ.....59S.193S full text sources ADS |

Preparation of a General Catalogue of Trigonometric Parallaxes.

view Abstract Citations (4) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Preparation of a General Catalogue of Trigonometric Parallaxes. Jenkins, Louise F. Abstract It is now 16 years since the appearance of the second edition of the General Catalogue of Parallaxes and many inquiries have been received about a new edition. Investigation revealed that the trigonometric material is now about 50 per cent more than in the second edition. There is not available in published form any comparable increase in spectroscopic or dynamical parallaxes. The spectroscopic field seems to be at the present time in a state of flux and we are therefore limiting the new edition to trigonometric parallaxes. The punched-card machines at Yale facilitated the intercomparison of the different series of parallaxes and of their probable errors. In general the new comparisons confirmed Dr. Schlesinger's scheme of corrections used for the second edition. One characteristic discovered in the course of these comparisons, and confirmed by a comparison with the spectroscopic parallaxes of the 1935 catalogue, is that in some cases the smaller parallaxes show a dependence of the correction needed on the size of the parallax itself. This is not true of the larger parallaxes. We have adopted precepts depending for the larger parallaxes on the trigonometric comparisons, and for the smaller parallaxes with greater weight on the spectroscopic comparisons. Though these corrections are in some cases very small, it seemed well to apply the indicated correction thus eliminating the dependence upon the source in the final value used. The same corrections for galactic latitude were used as in the 1935 catalogue. The precepts for correcting the probable errors were determined by a least-squares solution. New comparisons using the corrected values of the parallaxes show satisfactory improvement. Probable users of this catalogue can be grouped into two classes, those who wish a value for the parallax of the star and those who wish to be able to refer to the sources of such a value. We are therefore giving on one page a line of information about each star; position, magnitude, spectral type, proper motion and adopted absolute parallax formed by the precepts given. On the opposite page will be given the individual determinations of the relative parallax for each star, except that if the two components of a double star have been observed separately or two determinations of a parallax have been made at one observatory, the separate values have been combined into one value, with the weight assigned corresponding to the probable error of the more accurate value. The observatory is listed and the weight with which that value enters the final value of the parallax. We are indebted to many colleagues for their assistance in making the final result possible: to those who sent manuscript lists of parallaxes not yet published, to Dr. Kuiper who contributed largely in supplying lacking spectra and revised magnitudes for numerous fainter stars, to Dr. Vyssotsky who also supplied spectra for a long list of stars, and to Dr. Schilt who gave many valuable suggestions. We record with thanks the generous help of Dr. van Woerkom in the planning and supervision of the work of the punched card machines and our indebtedness to Dr. Brouwer who throughout has given of his time and thought in the guidance of the work. At the present time the catalogue is being typed for photo-offset reproduction. Yale University Observatory, New Haven, Conn. Publication: The Astronomical Journal Pub Date: October 1951 DOI: 10.1086/106550 Bibcode: 1951AJ.....56..130J full text sources ADS |

Some characteristics of the spectra of F-, G-, and K-type stars.

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Some characteristics of the spectra of F-, G-, and K-type stars. Roman, Nancy G. Abstract At the Yerkes Observatory at the present time we are engaged in an extension of the Morgan-Keenan-Keilman system of spectral classification to all northern stars brighter than 5.5 visual magnitude. Although the work has not been completed, two results seem worthy of attention. Among the 168 stars studied having HD spectral types F~ to G~, there are 13 F~ giants, 29 G8 giants, 13 Ko giants, and only 12 giants of types F6, F8, Go, G2, and G5. That the scarcity of early G-type giants is real is shown clearly by a plot of colors against absolute magnitudes. Fourteen of the stars show a composite spectrum, usually consisting of a late-type giant and an A- or F-type star. Those with an A-type component are easily recognized by the characteristic appearance of the K-line but those with an F-type component simulate the spectra of normal early G-type giants. Capella, composed of an F6 star and a late G giant, is an excellent example of the latter type of system. The resulting composite spectrum can be distinguished from that of a G2 giant on low dispersion primarily by the strength of the CX. Since late- type giants are numerous and early G-type giants are scarce, a large percentage of the stars classed as early G-type giants are probably binaries with composite spectra. A number of giant and dwarf stars of types F~ to G~ show systematically weaker lines than other stars in the same position on the H-R diagram. Space velocities based on spectroscopic parallaxes and corrected for a solar motion of 20 km/sec were computed for 8~ stars of types F~ to G5. It was found that the speeds of the stars with strong lines show a maximum frequency between 10 and 20 km/sec with no stars having speeds larger than 70 km/sec. On the contrary, the speeds of the 40 stars with weaker lines show only a broad maximum between 30 and 6o km/sec; 8 of these stars have speeds greater than 70 km/sec. Verkes Observatory, Williams Bay, Wis. Publication: The Astronomical Journal Pub Date: October 1950 DOI: 10.1086/106403 Bibcode: 1950AJ.....55..182R full text sources ADS |

The absolute magnitudes of the early A-type stars from hydrogen line absorption.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The absolute magnitudes of the early A-type stars from hydrogen line absorption. Petrie, R. M. ; Maunsell, C. D. Abstract The intensities of H~ have been determined, by spectrophotometric measures, in the spectra of 165 stars of spectral types B8 to A3. The measures have been calibrated against absolute magnitudes derived from trigonometric, spectroscopic, dynamical, and cluster parallaxes. The equivalent width of H~ is found to be capable of predicting the absolute magnitude of a normal star, white dwarfs being excepted. The mean residual from the trigonometric parallaxes is Q'.'00I ~ "001. Spectroscopic absolute magnitudes are given for 165 A stars. Dominion Astrophysical Observatory, Victoria, B. C., Canada. Publication: The Astronomical Journal Pub Date: September 1949 DOI: 10.1086/106259 Bibcode: 1949AJ.....54..193P full text sources ADS |

Giant Binary Stars and the Mass-Luminosity Law

IT is well known that spectroscopic parallaxes are an index of stellar surface gravity, which in turn is functionally related to the mass and luminosity of a star. If, therefore, there exists a class of stars in which this functional relation differs from that found for the majority of stars, we should expect a lack of agreement of the mean trigonometric, dynamic and spectroscopic parallaxes of these stars.

The Russell-Moore discordant parallax stars.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Russell-Moore discordant parallax stars. Hynek, J. A. Abstract The discordance between the trigonometric and spectroscopic parallaxes of 52 giant binary pairs first pointed out by Russell and Moore1 is found to remain when the study is extended to additional visual pairs and to 47 spectroscopic binaries. A similar discordance is observed between the dynamic and spectroscopic parallaxes of 103 pairs, thus corroborating the trigonometric results. The failure of the mass-luminosity law for, at least, the brighter members of giant binary stars is strongly indicated. The evidence presented by all three types of parallax is consistent with the hypothesis that, as a class, the binary stars of the giant sequence are more than a magnitude brighter than normal giants, of nearly twice their radius, and of more than twice their mass. Excessive mass is indicated both by spectroscopic evidence and by direct determination by the usual double star method. There is some possibility that these stars are members of "population II." I.Masses of the Stars, p. 6o, 1940. Emerson MeMillin Observatory, Cleveland, Ohio Publication: The Astronomical Journal Pub Date: October 1948 DOI: 10.1086/106184 Bibcode: 1948AJ.....54...40H full text sources ADS |

The H-R diagram and space distribution of the members of the Ursa Major cluster.

Introduction. In two papers on the Ursa Major cluster, published in 1939, Smart examined the claim to cluster membership of 136 stars. He concluded that 42 of these stars are definitely members of the cluster while the status of 52 was doubtful. The purpose of this investigation has been to obtain spectroscopic parallaxes of these stars and, combining these with the remaining data in Smart's papers, to reexamine the question of the membership of the cluster and to give a revised H-R diagram. A number of stars with small proper motions, for which the data are inconclusive, have been excluded by the limits on the position angle residual of 100 for definite members and 200 for probable members. The more accurate spectroscopic parallaxes have also excluded a few stars; the number has been reduced to 32 definite members and 12 probable members. There are probably also several members south of ~3o0 which have not been considered in this investigation. Space distribution. The cluster has a fairly compact nucleus containing I I stars within nine parsecs. The remaining stars are scattered up to a distance of 135 parsecs from this nucleus. The Coma and the Hyades clusters are included in the volume of space occupied by the Ursa Major cluster; Praesepe and the Pleiades are almost within it. In contrast to the Ursa Major cluster, the Coma cluster contains about 30 stars of similar absolute magnitude, Praesepe and the Hyades, about 75, and the Pleiades, several hundred members, each in a region less than eight parsecs across. H-i? Diagram. Nine of the nucleus stars give a smooth main sequence; the others include a metallic line star, a peculiar A star, and probably a Go subdwarf. The latter was discovered in an attempt to find the fainter members of the cluster in the vicinity of the nucleus from their proper motion, and has no radial velocity. The outlying members are also primarily main sequence stars with no stars in the cluster earlier than Ao. The cluster also probably contains an Mo giant, six late G giants, two early F giants, and four peculiar stars. Dynamical considerations. If the distribution of velocities near the sun were actually random, 575 of the stars in the Bright Star Catalogue within a hundred parsecs would have speeds within 4 km/sec of the cluster speed. However, only four of these would be moving within 100 of the direction of the cluster motion. A calculation of the effect of stellar encounters shows that a cluster star will probably change its kinetic energy with respect to the nucleus of the cluster by less than 20 per cent in 3 X IO~ years. This means that the life time of the cluster is of the same order as the galactic time scale. Yerkes Observatory, Williams Bay, Wis.

The Systematic and Accidental Errors of Spectroscopic Parallaxes.

view Abstract Citations (6) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Systematic and Accidental Errors of Spectroscopic Parallaxes. Russell, Henry Norris ; Moore, Charlotte E. Abstract I. The stars for which trigonometric and spectroscopic parallaxes are available were divided into eight groups of approximately equal number, in order of the "reduced" spectroscopic parallaxes and of the reduced proper motions, and the mean reduced spectroscopic and trigonometric parallaxes were compared. Tue deviations from linear correlation between the two are no larger than can be attributed to the accidental and sampling errors-both for the biased and impartial groupings and also for four ranges of spectral class among main-sequence stars, for all these together, and for giants. To distinguish between the results of the assumptions of linear correlation between the absolute mag- nitudes and between the reduced parallaxes would demand several times the observa- tional data now available (i 140 stars). For stars differing greatly in absolute magni- tude from the general mean (such as Groombridge 1830), these linear correlations are probably invalid; and the data are at present insufficient for a reliable calibration. II. The dispersion constants for the reduced parallaxes have been redetermined by analysis of these mean values (Table 4) and compared with those obtained by our earlier correlation analysis (Table 5). The factor i/i, by which the differences of the tabular spectroscopic absolute magnitude from the mean for the spectral subclass must be multiplied in order to obtain an impartial calibration, comes out consistently larger by the latter method. III. The correlation between the reduced parallaxes and proper motions (which is equivalent to that between the absolute magnitude M and H = in + 5 log j~) shows that, for groups brighter and fainter than the normal for the spectral subclass, = 0.74 for main-sequence stars and o.66 for giants. Comparison of giants and dwarfs gives ~M/~H = 0.69; of stars in different parts of the main sequence, o.8o. IV. Unavoidable deviations of spectroscopic absolute magnitudes from the true values may arise from physical causes within the stars, such as differeiices in the relative abundance of hydrogen and heavy elements, either in the interior or in the atmosphere, and differences in the contribulion of negative hydrogen ions to the general opacity. These differences may account for a considerable portion of the apparent "errors" of spectroscopic parallaxes. V. These effects, combined with a correlation between the masses and the space- velocities of the stars, may cause grouping by H to be systematically different from one by M; but this appears inadequate to account for the systematic differences mentioned above. VI. Since no conclusive reasons have been found for preferring one of the sets of con- stants described in (II) to the other, weighted means have been taken, and the remain- ing dispersion constants have been determined with the aid of these. Results for the reduced parallaxes appear in Table 9; and the corresponding constants for the absolute magnitudes (derived on the assumption that these have a normal distribution), in Table io. The mean-square difference 0 between the spectroscopic absolute magnitudes, M~, as published in Mt. W. Contr. No. 511, and the true values is ±o'~'48 for main-sequence stars as a whole and ± o~ for giants. Joy's values, derived from double stars and clusters, are in substantial agreement with this. To obtain an impartial calibration, * Contributions from the Mount Wilson Observatory, Carnegie Institution of Wash- ington, No. 636. `Research associate of the Carnegie Institution of Washington Publication: The Astrophysical Journal Pub Date: November 1940 DOI: 10.1086/144226 Bibcode: 1940ApJ....92..354R full text sources ADS | Related Materials (1) Reprint: 1940CMWCI.636....1R

Dr. W. E. Harper

DR. WILLIAM EDMUND HABPBB, who died on June 14, at the age of sixty-two, had been director of the Dominion Astrophysical Observatory since 1936. Dr. Harper was born in Ontario on March 20, 1878, and graduated from the University of Toronto in 1906. On that day he received word of his appointment to the staff of the Dominion Observatory at Ottawa. For thirteen years he was engaged there in the determination of the orbits of spectroscopic binaries, and on his transfer to Victoria, when the Government sponsored the 72-inch reflector, he continued the same work. In 1924 he was made assistant director, and finally director in 1936. From the time of his graduation until his death he was intimately associated with the development of astronomy in Canada. Before his death he had determined the orbits for more than a hundred binaries. No other astronomer has approached this number. His contributions to this part of astronomy constitute approximately one quarter of the known orbits. Among other major pieces of work were the determination of 1,100 spectroscopic parallaxes and the measurement of over 7,000 plates for radial velocity.

Discovery of a Near New Star

DR. OTTO STRTUVE, Yerkes Observatory, reports the discovery of a new star to which the name Wolf 424 has been assigned. It is described as of the twelfth visual magnitude, and its spectrum is of the very late M-type. As is well known, it is possible to determine stellar distances to a fair degree of accuracy from their spectral type. The examination of the spectra of stars of known distances shows that the intensities of certain lines in their spectra vary with the true luminosity of the stars. Conversely, by studying lines in the spectra of stars, the real light output can be estimated, and this, combined with the star's apparent brightness, furnishes the necessary data for determining the distance. In the case of the new star, this method has been applied, and the spectroscopic parallax so found shows that it is probably closer to us than a Centauri. It should be pointed out, however, that there is considerable doubt about the true distance, for various reasons. Very great accuracy in determining the intensities of the lines is essential, and in addition, if, as is possible, the star is a very close unresolved binary, this would vitiate the results to some extent. There is no doubt about the star being fairly close to us, for which reason its trigonometrical parallax can be determined in about six months and its distance found by this independent method. Until this has been done, it is advisable to suspend judgment regarding Dr. Struve's conjecture that it may be the nearest star.