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NASA NTRS1994

The initial mass function for massive stars in the Magellanic Clouds. 2: Interstellar reddening toward 14 OB associations

We have used UBV CCD photometry to determine the interstellar reddening toward 14 OB associations in the Magellanic Clouds. The two reddening-free indices available in the UBV system were used to obtain the reddening estimates. The mean color excesses of the associations range from E(B-V) = 0.01-0.26 mag in the Large Magellanic Cloud (LMC) and from E(B-V) = 0.06-0.25 mag in the Small Magellanic Cloud (SMC). We have modeled the observed scatter in the color excesses of individual stars within the associations and find that statisically significant differential reddening exists in at least some of the associations.

Hill, Robert J.↗

NASA NTRS1994

The initial mass function for massive stars in the Magellanic Clouds. 3: Luminosity and mass functions for 14 OB associations

We have used UBV photometry of stars in 14 associations in the Large and Small Magellanic Clouds (LMC/SMS) (Hill, Madore, & Freedman) to derive luminosity and mass functions for the most massive stars. The main-sequence luminosity functions for the associations are quite similar, having an average slope of s = 0.03 +/- 0.06. The mass functions for the associations have slopes that span similar ranges about a common mean for both the LMC and SMC and there is no strong evidence for a significant variation in the slopes from one association to another. Accordingly, metal abundance does not appear to have a strong effect on the initial mass function (IMF), at least for the range in metallicity observed between the Magellanic Clouds. The average slope of the IMF for the Magellanic Cloud associations is Gamma = -2.0 +/- 0.5 for M greater than 9 Solar Masses. The range in the derived slopes is more likely due to the large uncertainties associated with the calculations of the mass functions, rather than to real variations in the IMF. There may be some evidence for a decrease in the slope of the IMF at masses below 9 Solar Masses, but incompleteness and the larger photometric errors associated with the faintest stars make this conclusion tentative.

Hill, Robert J.↗

NASA NTRS1993

Spacecraft fault tolerance: The Magellan experience

Interplanetary and earth orbiting missions are now imposing unique fault tolerant requirements upon spacecraft design. Mission success is the prime motivator for building spacecraft with fault tolerant systems. The Magellan spacecraft had many such requirements imposed upon its design. Magellan met these requirements by building redundancy into all the major subsystem components and designing the onboard hardware and software with the capability to detect a fault, isolate it to a component, and issue commands to achieve a back-up configuration. This discussion is limited to fault protection, which is the autonomous capability to respond to a fault. The Magellan fault protection design is discussed, as well as the developmental and flight experiences and a summary of the lessons learned.

Kasuda, Rick↗

NASA NTRS1993

Magellan attitude control mission operations

From the Martin Marietta Astronautics Group base in Denver, Colorado, spacecraft engineers have been operating the Magellan spacecraft for the past three and one half years, along with the Jet Propulsion Laboratory, for NASA. The spacecraft team in Denver is responsible for the health of the vehicle, from command generation to evaluation of engineering telemetry. Operation of the spacecraft's Attitude and Articulation Control Subsystem (AACS) has specifically posed several in-flight challenges. This system must provide accurate pointing of the spacecraft throughout each 3.2 hour orbit which typically consists of 5 - 9 discrete maneuvers. Preparation of bi-weekly command sequences, monitoring execution, and trending of subsystem performance is of paramount importance, but in-flight anomalies have also demanded the attention of AACS engineers. Anomalies are often very interesting and challenging aspects of a project, and the Magellan mission was no exception. From the first unsuccessful attempts to perform a starscan, to spacecraft safing events, much has been experienced to add to the `lessons learned' from this mission. Many of Magellan's in-flight experiences, anomalies, and their resolutions are highlighted in this paper.

Dukes, Eileen M.↗

NASA NTRS1994

Orbital maneuvers: Magellan aerobrakes into Venus' atmosphere

The aerobraking orbital activities of Magelland during the gravity mapping of Venus are discussed. The goal of aerobraking was to circularize Magellan's orbit. By aerobraking the spacecraft into a nearly circula orbit, the Magellan team was able to provide scientists with a different data set to deepen their understanding of what is going on beneath Venus' surface. Before undertaking its gravity-mapping mission, Magellan completed three cycles of radar mapping. This repeated coverage allowed the spacecraft to see some of Venus' geologic features from different viewing angles. Various aspects of the mission are discussed, and maps of Venus are presented.

Doody, David↗

NASA NTRS1992

Ionized carbon (CII) in the Magellanic Clouds

We present preliminary results of recently obtained observations of the important cooling line of singly ionized carbon in the Magellanic Clouds. Three large Magellanic Cloud (LMC) and six HII region/CO cloud complexes have been detected and mapped. Comparison shows that the strength and distribution of (CII) regions is well-correlated with those of dust complexes emitting far-infrared radiation, but not with molecular cloud complexes traced by CO emission. The results confirm that photo-dissociation processes are of relatively greater importance in Magellanic Cloud star formation regions than in Galactic regions.

Israel, F. P.↗

NASA NTRS1998

Radio Occultation Studies of Venus' Atmosphere with Magellan

We have been conducting a systematic study of the middle and lower atmosphere of Venus through analysis of 20 radio occultation experiments conducted with the Magellan spacecraft between October, 1991, and August, 1994. These studies have revealed a rich but sparsely sampled trove of information regarding the structure, composition and dynamics of the Venus atmosphere. The five sets of experiments sampled a variety of latitudes. Basic results include vertical profiles of: (1) electron density in the ionosphere, (2) pressure, temperature, density, and static stability in the neutral atmosphere (from 33 km to 98 km), and (3) sulfuric acid vapor (H2SO4) abundance below the main cloud deck. Further analysis of the temperature profiles led to the discovery of small vertical-scale gravity waves in the neutral atmosphere. The retrieved profiles show intriguing zonal variations that might be due to planetary- scale waves. During the performance period of this grant, we have concentrated on reanalyzing the 15 experiments conducted in 1994 using improved trajectory files for Magellan provided by JPL, obtaining more reliable results, and on conducting an error analysis of the derived profiles. In addition, we have begun an analysis of microwave emission maps of Venus obtained at the Very Large Array (VLA) in April, 1996. This report is organized as follows: A summary of results is presented, giving representative examples of the various physical profiles retrieved from all the Magellan radio occultation studies, emphasizing latitudinal variations evident in the data. Next, a preliminary analysis of the VLA maps is given. A summary of activities follows the scientific results, detailing papers published and presented at various conferences. This report concludes with a "Conclusions and Suggestions for Future Work" section.

Jenkins, Jon M.↗

NASA NTRS1999

A Reconnaissance of the 900-1200 A Spectra of Early O Stars in the Magellanic Clouds

Far-UV spectrograms of ten very hot stars in the Magellanic Clouds were obtained with the Hopkins Ultraviolet Telescope during the Astro-2 mission in March 1995. Very few normal OB stars were observed during Astro-1, and the only significant prior sample of such objects in this wavelength range was that obtained by Copernicus of stars near the Sun. The Magellanic Cloud sample offers the advantages of low reddening, a range in metallicity, and more extreme temperatures and luminosities than represented in the near solar neighborhood. Several interesting phenomena were found in the HUT MC sample, including very strong O VI wind profiles in O3 spectra; anomalous CNO wind features corresponding to abundances altered by stellar nucleosynthesis; weak wind features due to the metal deficiency of the Small Magellanic Cloud; and interstellar molecular hydrogen features originating in the MCs. The results were presented and discussed as a small atlas, and they were shown at the Pittsburgh AAS meeting in June 1995. A correlative atlas of Copernicus data was also prepared and published under the auspices of this grant. These publications will serve as resources for the characterization of the FUSE observations of related objects to hopefully be obtained soon. I believe that the large differences among the strong wind features in the HUT data, corresponding to CNO and systemic metallicity effects, are amenable to some relative quantitative analysis, and I shall endeavor to promote such in conjunction with HST data at longer wavelengths for the same stars (which has also not yet been completely analyzed) at a future opportunity.

Walborn, Nolan↗

NASA NTRS1990

Magellan Press Conference (1 of 2)

Live footage shows several speakers participating in the Magellan Press Conference. Speakers include the Director of Solar System Exploration Division West Huntress, Magellan Project Manager Tony Spear, Spacecraft Team Chief W. Ledbetter, Radar System Chief Engineer T. Johnson, and Magellan Project Manager from Hughes Aircraft Co. T. McCarthy. The speakers discuss the Venus Orbiting Insertion (VOI), radar system components, spacecraft development, mission objectives, and the flight plans. This is tape 1 of 2; tape 2 has a report number NONP-NASA-VT-2000036566.

Source record↗

NASA NTRS2000

Aerobraking at Venus and Mars: A Comparison of the Magellan and Mars Global Surveyor Aerobraking Phases

On February 4, 1999 the Mars Global Surveyor spacecraft became the second spacecraft to successfully aerobrake into a nearly circular orbit about another planet. This paper will highlight some of the similarities and differences between the aerobraking phases of this mission and the first mission to use aerobraking, the Magellan mission to Venus. Although the Mars Global Surveyor (MGS) spacecraft was designed for aerobraking and the Magellan spacecraft was not, aerobraking MGS was a much more challenging task than aerobraking Magellan, primarily because the spacecraft was damaged during the initial deployment of the solar panels. The MGS aerobraking phase had to be completely redesigned to minimize the bending moment acting on a broken yoke connecting one of the solar panels to the spacecraft. Even if the MGS spacecraft was undamaged, aerobraking at Mars was more challenging than aerobraking at Venus for several reasons. First, Mars is subject to dust storms, which can significantly change the temperature of the atmosphere due to increased solar heating in the low and middle altitudes (below 50 km), which in turn can significantly increase the density at the aerobraking altitudes (above 100 km). During the first part of the MGS aerobraking phase, a regional dust storm was observed to have a significant and very rapid effect on the entire atmosphere of Mars. Computer simulations of global dust storms on Mars indicate that even larger density increases are possible than those observed during the MGS aerobraking phases. For many aerobraking missions, the duration of the aerobraking phase must be kept as short as possible to minimize the total mission cost. For Mars missions, a short aerobraking phase means that there will be less margin to accommodate atmospheric variability, so the operations team must be ready to propulsively raise periapsis by tens of kilometers on very short notice. This issue was less of a concern on Venus, where the thick lower atmosphere and the slow planet rotation resulted in more predictable atmospheric densities from one orbit to the next.

Lyons, Daniel T.↗

NASA NTRS2013

The HERschel Inventory of the Agents of Galaxy Evolution in the Magellanic Clouds, a HERschel Open Time Key Program

We present an overview or the HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) in the Magellanic Clouds project, which is a Herschel Space Observatory open time key program. We mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 micron with the Spectral and Photometric Imaging Receiver (SPIRE) and Photodetector Array Camera and Spectrometer (PACS) instruments on board Herschel using the SPIRE/PACS parallel mode. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC. The far-infrared and submillimeter emission is an effective tracer of the interstellar medium (ISM) dust, the most deeply embedded young stellar objects (YSOs), and the dust ejected by the most massive stars. We describe in detail the data processing, particularly for the PACS data, which required some custom steps because of the large angular extent of a single observational unit and overall the large amount of data to be processed as an ensemble. We report total global fluxes for LMC and SMC and demonstrate their agreement with measurements by prior missions. The HERITAGE maps of the LMC and SMC are dominated by the ISM dust emission and bear most resemblance to the tracers of ISM gas rather than the stellar content of the galaxies. We describe the point source extraction processing and the critetia used to establish a catalog for each waveband for the HERITAGE program. The 250 micron band is the most sensitive and the source catalogs for this band have approx. 25,000 objects for the LMC and approx. 5500 objects for the SMC. These data enable studies of ISM dust properties, submillimeter excess dust emission, dust-to-gas ratio, Class 0 YSO candidates, dusty massive evolved stars, supemova remnants (including SN1987A), H II regions, and dust evolution in the LMC and SMC. All images and catalogs are delivered to the Herschel Science Center as part of the conummity support aspects of the project. These HERITAGE images and catalogs provide an excellent basis for future research and follow up with other facilities.

AGENTS↗

NASA NTRS2017

Observing Strategies for Focused Orbital Debris Surveys Using the Magellan Telescope

A breakup of the Titan 3C-17 Transtage rocket body was reported to have occurred on June 4th, 2014 at 02:38 UT by the Space Surveillance Network (SSN). Five objects were associated with this breakup and this is the fourth breakup known for this class of object. There are likely many more objects associated with this event that are not within the Space Surveillance Network's ability to detect and have not been catalogued. Several months after the breakup, observing time was obtained on the Magellan Baade 6.5 meter telescope to be used for observations of geosynchronous (GEO) space debris targets. Using the NASA Standard Satellite Breakup Model (SSBM), a simulated debris cloud of the recent Transtage breakup was produced and propagated forward in time. This provided right ascension, declination, and tracking rate predictions for where debris associated with this breakup may be more likely to be found in the sky over Magellan for our observing run. Magellan observations were then optimized using the angles and tracking rates from the model predictions to focus the search for Transtage debris. Data were collected and analysed and preliminary comparisons made between the number of objects detected and the number expected from the model. We present our results here.

Frith, James↗

NASA NTRS2017

Observing Strategies for Focused Orbital Debris Surveys Using the Magellan Telescope

Frith, James↗

NASA NTRS2023

An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog

The nature of molecular clouds and their statistical behavior in subsolar metallicity environments are not fully explored yet. We analyzed data from an unbiased CO (J = 2–1) survey at the spatial resolution of ∼2 pc in the northern region of the Small Magellanic Cloud with the Atacama Compact Array to characterize the CO cloud properties. A cloud-decomposition analysis identified 426 spatially/velocity-independent CO clouds and their substructures. Based on the cross-matching with known infrared catalogs by Spitzer and Herschel, more than 90% CO clouds show spatial correlations with point sources. We investigated the basic properties of the CO clouds and found that the radius–velocity linewidth (R–σ v ) relation follows the Milky Way-like power-law exponent, but the intercept is ∼1.5 times lower than that in the Milky Way. The mass functions (dN/dM) of the CO luminosity and virial mass are characterized by an exponent of ∼1.7, which is consistent with previously reported values in the Large Magellanic Cloud and in the Milky Way.

Local Group↗

NASA NTRS1971

Cepheid variables and the Magellanic Clouds.

The Magellanic Cloud variables differ from variables in the Galaxy by the number of variables at different periods, by the period-amplitude relation, and by the mean color. Schematic evolutionary tracks are used to demonstrate how a proposed difference between Galactic evolution and Small Magellanic Cloud evolution might be responsible for the observed mean colors and frequencies of occurrence of cepheid variables with different periods. The frequency of short-period cep heids is seen to be a very sensitive indicator of some, not yet fully understood, aspect of abundances. It is demonstrated that the characteristic second-bump feature appearing in the light curves of cepheids with the period range from 7 to 15 days can be used to determine stellar mass and radius on the basis of calculations of interior motions.-

Christy, R. F.↗

NASA NTRS1976

Emission nebulae in the Magellanic Clouds. I - The H II regions

A review of optical and radio studies of the H II regions in the Magellanic Clouds is presented. Recent studies are emphasized, particularly optical studies of the kinematics, spectra, and chemical composition. The implications of the studies for the understanding of the evolution of stars and galaxies in general, and the Magellanic Clouds in particular, are noted. Suggestions for future work are also given.

Dufour, R. J.↗

NASA NTRS1977

The chemical composition of three planetary nebulae in the Magellanic Clouds

The paper studies the detailed spectral characteristics of the planetary nebulae N97 and N153 in the Large Magellanic Cloud (LMC), the planetary nebula N67 in the Small Magellanic Cloud (SMC), and the small H II regions N9, N61, and N81 in the SMC. Electron temperatures and densities for each nebula are derived from emission-line strengths determined by photographic spectrophotometry, and relative abundances are estimated for H, He, N, O, Ne, Ar, and S. The results show that: (1) N67 has a 60% overabundance in He/H while N97 and N153 have approximately normal He/H values; (2) all three planetaries have N/H values comparable to those of galactic planetaries but substantially higher than found in the H II regions of their respective Cloud; (3) the O/H values in the planetaries are similar to or lower than those in the H II regions of the respective Cloud; (4) the O/Ne, O/S, and O/Ar ratios in the two LMC planetaries are comparable to those in galactic planetaries; (5) the compositions of the small H II regions in the SMC are nearly identical to those of previously studied large H II regions in the same Cloud; and (6) the He/H ratio of the interstellar gas in the SMC is about 25% less than that in the Galaxy. It is concluded that most of the N abundance in both Clouds arose from nucleosynthesis sources other than planetary nebulae.

Dufour, R. J.↗

NASA NTRS1978

On two new X-ray sources in the SMC and the high luminosities of the Magellanic X-ray sources

The discovery of two new X-ray sources, SMC X-2 and SMC X-3, in the Small Magellanic Cloud is reported. They have hard spectra, and their luminosities in the energy range 2-11 keV are 1.0 and 0.7 by 10 to the 38th power erg/sq cm per sec, respectively. It is shown that the luminosity distribution of the known Magellanic X-ray sources, which are now nine in number, is shifted toward higher luminosities with respect to that of similar sources in the Galaxy, and that the cause of the shift is probably an underabundance of heavy elements in the material accreted by the X-ray sources.

Clark, G.↗