Harvard College Observatory Research Articles

E.C. Pickering, Lydia Hinchman, Harlow Shapley, and the Beginning of Graduate Work at the Harvard College Observatory

E.C. Pickering, Lydia Hinchman, Harlow Shapley, and the Beginning of Graduate Work at the Harvard College Observatory

Oscillations in EUV emission lines during a loop brightening

Oscillations in the emission in the ultraviolet lines of Cii, Oiv, and Mg x, detected by the Harvard College Observatory EUV spectroheliometer on Skylab are observed on August 7, 1973, during a loop brightening. The intensity of the EUV lines varies with a period of 141 s during the time of enhanced intensity of the coronal loop, lasting 10 min. The periodic oscillation is not only localized in the loop region but extends over a larger area of the active region, maintaining the same phase. We suggest that the intensity fluctuation of the EUV lines is caused by small-amplitude waves, propagating in the plasma confined in the magnetic loop and that size of the loop might be important in determining its perferential heating in the active region.

Period Changes in Magellanic Cloud Cepheids

It has been found possible to obtain information on period change in data on 115 cepheid variable stars in the Magellanic Clouds (84 LMC cepheids and 31 SMC cepheids). Harvard Observatory data of the period 1910 to 1950 (collated by Payne-Gaposchkin and Gaposchkin) are combined with Dunsink Observatory observations carried out by C.J. Butler in 1966/67 and with South African Astronomical Observatory observations covering the years 1975–1977 by Martin, Thomas, Carter and Davies to derive mean periods for the intervals between the various data sets. Using these new periods in conjunction with the very accurate Harvard periods, seperate estimates of the time averaged fractional change of period per day, d/dt (ln P), with corresponding estimated errors, could be evaluated for two epochs, one around 1950 and the other around 1971. It was found that 70 stars give rates of change of period that are not significantly different from zero, that 20 stars have two values of rate of change of period that are in agreement at the two epochs (indicative of secular period change), while 22 stars give two disparate values of rate of change of period (indicative of irregular period changes).

Orbital periods of novae before eruption

view Abstract Citations (48) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Orbital periods of novae before eruption. Schaefer, B. E. ; Patterson, J. Abstract The collection of archival plates at Harvard College Observatory was used to search for the eclipse periods of two novae (BT Mon and DQ Her) both before and after the outburst. The eclipse period of BT Mon is manifest in the data both before and after its 1939 eruption. The pre-eruption eclipse period is 0.3338010 d, which is 40 parts per million shorter than the modern period. With reasonable assumptions concerning the angular momentum carried off by the ejected material, this provides a dynamical measure of the mass of the ejecta, which is estimated to be 0.00003 solar mass. It is found that the specific angular momentum of the shell around BT Mon cannot be greatly in excess of the specific orbital angular momentum of the white dwarf. Analysis of all available data fails to specify the pre-eruption eclipse period of DQ Her, presumably because the light curve is badly smeared by the long photographic exposure times. Publication: The Astrophysical Journal Pub Date: May 1983 DOI: 10.1086/160992 Bibcode: 1983ApJ...268..710S Keywords: Angular Momentum; Eclipsing Binary Stars; Light Curve; Novae; Stellar Mass Ejection; Astronomical Photography; Stellar Envelopes; Stellar Magnitude; White Dwarf Stars; Astrophysics full text sources ADS | data products SIMBAD (2)

EUV arcades: Signatures of filament instability

We have examined seven active regions of the Skylab period in the EUV (Harvard College Observatory), and in Hα and K3 (Observatoire de Meudon, spectroheliograms and patrols) in order to elucidate the magnetic geometry in the coronal environment of filaments. We have also looked for signatures of magnetic reconfigurations associated with instabilities (i.e. velocities or disappearances) of filaments. Out of sixteen Hα filaments observed, six were stable (lifetime ≥ 48h). All the filaments lay within coronal cavities as seen in lines formed above 1.5 × 106 K (Mgxλ625, Sixiiλ521, Fexviλ417, Fexvλ361). None of the stable filaments had arcades or arches spanning the cavities except (sometimes) at the ends of the filaments. On the other hand, most (8/10) of the unstable filaments (having concurrent Doppler shifts or a subsequent DB within 24h) had arcades or single arches spanning their cavities. The arches were observed in EUV lines with formation temperatures as low as 2–4 × 105 K (Oivλ554, Oviλ1032, Ne viiλ465), as well as in hotter lines. A statistical test shows that the arcade/instability vs non-arcade/stability association is significant at the 99% confidence level. We suggest 2 types of scenario relating arcades to instabilities. The more preferable scenario is closely related to the Kuperus/Van Tend model of filament disruptions.

Probable optical counterpart of a γ-ray burster

I describe here 1.6 × 107 s (over half a year) of optical monitoring of three γ-ray burst positions using the collection of archival plates at the Harvard College Observatory. The search has uncovered the probable optical counterpart for the 19 November 1978 γ-ray burster on a blue emulsion plate exposed in 1928. The optical flash observed on the 1928 plate has mB ∼ 3, for an assumed duration of 1 s. Optical searches indicate that the absolute magnitude of the γ-ray burst system at quiescence is fainter than 13. A recurrence rate of ∼10−7.5 s−1 is found from the γ-ray and optical data. A recurrence rate this high rules out any model which uses a collision between a neutron star and an asteroid-like body as well as any model which requires accretion from the interstellar matter onto a neutron star.

Hypersurfaces of constant mean extrinsic curvature: Sian M. Stumbles, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge CB3 9EW England; and Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory, Cambridge, Massachusetts 02138

Hypersurfaces of constant mean extrinsic curvature: Sian M. Stumbles, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge CB3 9EW England; and Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory, Cambridge, Massachusetts 02138

ECLIPSING BINARIES WITH NODAL MOTION - ARCHIVAL DATA

ABSTRACT This paper presents a study of the three eclipsing binaries IU Aur, NQ Her, and AY Mus for times before 1943. The data were obtained from examination of archival photographic plates in the collection of Harvard College Observatory. IU Aur was found to have an amplitude of 0m.18 ± 0m.05 in 1890-04 and 0m.24 ± 0m.04 in 1931-36. These amplitudes are used to derive an inclination of the eclipsing binary's orbital plane of 61° ± 2° and 66° ± 2°, respectively. A nodal rotation period of 150 years is most likely. The angle between the orbital planes of the eclipsing binary and the third body is 15°.8. The previous reported period of NQ Her, 0d.870218, is shown to be erroneous, so that previous claims of nodal motion in this system are unfounded. AY Mus was found to be eclipsing with a period of 3d.20559 for the years 1897 to 1943. This confirmation of the eclipsing nature, when combined with a 1973 observation that AY Mus no longer eclipses, suggests that nodal motion is the cause for the stoppage of eclipse.

UV Emitting Spicules

Extreme ultraviolet observations of the chromospheric network in a coronal hole obtained in 1973 by the Harvard College Observatory experiment aboard Skylab are analyzed. Upper and lower limits to the actual emission measure in UV spicules have been obtained, and the consistency of the derived values with the hypothesis that UV spicules are Hα spicules falling back after being heated is discussed.

A comparison of high-temperature flare models with observations and implications for the low-temperature flare

EUV data from the Harvard College Observatory and Naval Research Laboratory instruments on board the Skylab Apollo telescope mount, together with SOLRAD 9 X-ray data, are analyzed in order to empirically deduce the variation of emission measure with temperature in the atmosphere of a number of solar flares. A 'mean' differential emission measure profile Q(T) for a flare is constructed which is then compared with the profile predicted by a number of theoretical models. It is found that realistic flare models must include both conductive and radiative terms in the energy equation, and that hydrodynamic terms may be important at low temperatures. The implications of the results obtained are discussed for flare models in general and it is shown that the inclusion of the conductive term into models which have hitherto neglected it can perhaps resolve some of the observational difficulties with such models.

The pre-maximum light curve of the slow Nova Vulpeculae 1979

view Abstract Citations (30) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The pre-maximum light curve of the slow Nova Vulpeculae 1979. Liller, M. H. ; Liller, W. Abstract Blue-sensitive plates from the Harvard College Observatory archival collection show that Nova Vulpeculae 1979 began its recent outburst in late 1977 and may not have yet reached maximum brightness. Prior to 1977 the star varied irregularly between B = 14.5 and B = 16.6. Publication: The Astronomical Journal Pub Date: September 1979 DOI: 10.1086/112550 Bibcode: 1979AJ.....84.1357L Keywords: Light Curve; Novae; Stellar Magnitude; Astronomical Photography; Astronomy; Light Curves:Novae; Nova PU Vulpeculae; Nova Vulpeculae 1979 full text sources ADS | data products SIMBAD (2)

0246+18: A VARIABLE STAR SUPERPOSED ON A BRIGHT GALAXY

ABSTRACT The composite object 0246+18, which consists of a bright galaxy with a star superposed on it, has been observed to be optically variable. Data obtained from the archival plate collection at the Harvard College Observatory indicate that the object has a total range ΔB ≥1m.5.. Photoelectric photometry of this source reveals changes of at least 0m.11 on consecutive nights. The UBV colors are consistent with the hypothesis that the optical variations are due to the superposed star. There is no convincing evidence that the nucleus of this galaxy is optically active.

Lyman continuum observations of solar flares

A study is made of Lyman continuum observations of solar flares, using data obtained by the Harvard College Observatory EUV spectroheliometer on the Apollo Telescope Mount. We find that there are two main types of flare regions: an overall ‘mean’ flare coincident with the Hα flare region, and transient Lyman continuum kernels which can be identified with the Hα and X-ray kernels observed by other authors. It is found that the ground level hydrogen population in flares is closer to LTE than in the quiet Sun and active regions, and that the level of Lyman continuum formation is lowered in the atmosphere from a mass column density m ≈ 5/sx 10−6 g cm−2 in the quiet Sun to m ≈ 3/sx 10−4 g cm−2 in the mean flare, and to m ∼ 10−3g cm−2 in kernels. From these results we derive the amount of chromospheric material ‘evaporated’ into the high temperature region, which is found to be ∼- 1015g, in agreement with observations of X-ray emission measures. A comparison is made between kernel observations and the theoretical predictions made by model heating calculations, available in the literature; significant discrepancies are found between observation and current particle-heating models.

The occultation of ϵ Gem by Mars as observed from Agassiz Station

Observations of the April 8, 1976 occultation of ϵ Gem by Mars made at the Agassiz Station of the Harvard College Observatory have been analyzed to yield temperature profiles of the Martian atmosphere for number densities between 10 13 and 10 15 cm −3. Pronounced wavelike structure is evident in both immersion and emersion profiles, with a peak-tto-peak variation of up to 50°K and a vertical scale of 20 km.

Edward C. Pickering, the Henry Draper Memorial, and the beginnings of astrophysics in America

Summary Henry Draper, one of America's pioneer astrophysicists, launched a great period of advancement in astrophysics in 1872 when he succeeded in obtaining a photograph of a stellar spectrum exhibiting absorption lines. Shortly after his death in 1882, his widow established the Henry Draper Fund at the Harvard College Observatory, where Edward C. Pickering and his assistants began a long-range program of photographing, measuring, and classifying the spectra of the stars. As a result, Harvard was able to establish itself as the foremost institution in the United States for astrophysical research. Pickering's investigation culminated in the publication of ‘The Henry Draper Catalogue’, in which nearly a quarter of a million stellar spectra are measured and classified. The classification scheme embodied in the Draper catalogue is still heavily relied on today by all astrophysicists, and the Henry Draper Memorial has become a milestone in the history of astrophysics.

1418 + 54 - A new, violently variable BL Lacertae object

view Abstract Citations (26) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 1418+54: a new, violently variable BL Lacertae object. Miller, H. R. Abstract The new BL Lacertae object, 1418 + 54, has been found to exhibit large-amplitude optical variations on a time scale of days to years. The historical light curve of this object, as determined from a search of the archival plate collection of the Harvard College Observatory, indicates that it has a total range of at least about 4.8 mag. The long-term optical variability does not exhibit any obvious periodicity and implies source dimensions of approximately 0.0016 pc or less based on light-travel-time arguments. The variations observed are consistent with a multievent source model, similar to that proposed by Dent (1972) to account for the radio variability of extragalactic objects. However, the observed rate of change in brightness of 1418 + 54 is not consistent with the hypothesis that the individual events are due to Type II supernova explosions. Publication: The Astrophysical Journal Pub Date: July 1978 DOI: 10.1086/182730 Bibcode: 1978ApJ...223L..67M Keywords: Astronomical Photometry; Bl Lacertae Objects; Light Curve; Optical Polarization; Astronomical Models; Data Reduction; Extragalactic Radio Sources; Astronomy; BL Lacertae Objects:Optical Variations full text sources ADS | data products SIMBAD (2)

The characteristics of impulsive solar EUV bursts

We examine a number of high time resolution intensity-time profiles of EUV impulsive bursts as observed by the Harvard College Observatory EUV Spectroheliometer carried aboard the Skylab Apollo Telescope Mount. These bursts are found to be synchronous (to within the instrumental time resolution of 5.5 s) in all wavelengths observed, corresponding to emissions from temperatures ranging from upper chromospheric to coronal. The distribution with temperature of a suitably defined emission measure parameter is also examined as a function of time throughout the bursts and a marked similarity in the shape of this distribution, both between different events and throughout the time history of any particular event, is noted. The significance of these observations for physical processes associated with EUV bursts is briefly discussed.

NATURE OF X‐RAY BURSTERS*

Annals of the New York Academy of SciencesVolume 302, Issue 1 p. 197-209 NATURE OF X-RAY BURSTERS* Herbert Gursky, Herbert Gursky Center for Astrophysics Smithsonian Astrophysical Observatory Harvard College Observatory Cambridge, Massachusetts 02138Search for more papers by this author Herbert Gursky, Herbert Gursky Center for Astrophysics Smithsonian Astrophysical Observatory Harvard College Observatory Cambridge, Massachusetts 02138Search for more papers by this author First published: December 1977 https://doi.org/10.1111/j.1749-6632.1977.tb37049.xCitations: 2 * This work was supported in part by NASA Contract NAS5–23282. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume302, Issue1Eighth Texas Symposium on Relativistic AstrophysicsDecember 1977Pages 197-209 RelatedInformation

Non-Equilibrium Excitation and Ionization of Be-Sequence Ions

Intensities of resonance and subordinate lines in C III and O V are calculated for several non-equilibrium states expected to occur in the solar atmosphere. In particular, cooling (recombination) phases of solar flares, and regions of mass flow such as coronal holes and the network offer conditions where non-equilibrium phenomena can be significant. In such situations, the ionization state may not be in equilibrium with the electron temperature. Detailed comparison is made with the ultraviolet observations from the Harvard College Observatory experiment on Skylab which show temporal variations as well as clear non-equilibrium enhancement of the ratio of the 2s2p 3P - 2p23P transition 2 1 1 to the resonance line 2s21S - 2s2p 1P in both C III and O V.

Density Sensitive Lines in the EUV Region

A search for density sensitive line ratios was made in the 1400 Å to 300 Å region of the solar spectra. The emergent intensity of resonance and subordinate lines from ions of the beryllium and boron isoelectrcnic sequence were calculated for typical solar plasmas. For individual ions, line, ratios which are sensitive to electron densities changes between 107 to 1013cm –3were selected. These line ratios were then compared to observations made by the Harvard College Observatory spectrometer aboard SKYLAB. From all the potential candidates only few are adequately observed to estimate electron densities. In particular the Mg VIII lines at 430 and 436 Å are good indicators of the coronal densities. Comparisons of the densities of coronal holes, flares, and active regions are made.