Showing papers by "Charles H. Townes published in 1994"
356 citations
TL;DR: In this paper, the central 100 parsecs of our Galaxy were studied and the importance of magnetic and gravitational forces, evidence for stellar formation and a central massive black hole, and the origin and nature of ionization, outflows and interstellar gas dynamics.
Abstract: The subject of this review is the central 100 parsecs of our Galaxy, with a strong focus on the central few parsecs. Observations of the electromagnetic spectrum over 13 orders of magnitude in wavelength show a broad range of phenomena involving a number of physical processes. We discuss the stellar and interstellar components, the importance of magnetic and gravitational forces, the evidence for stellar formation and a central massive black hole, and the origin and nature of ionization, outflows and interstellar gas dynamics.
195 citations
01 Jan 1994
TL;DR: In this article, the interior of the Sickle molecular cloud is only weakly excited by Galactic center standards and the exterior of the cloud is highly excited by ultraviolet light from hot stars that have recently formed in the Galactic center.
Abstract: We present new near-infrared, far-infrared, submillimeter, and millimeter wave spectroscopic data from the “Pistol” and “Sickle” region. Our data show that the interior of the Sickle molecular cloud is only weakly excited by Galactic center standards. The exterior of the cloud is highly excited, and we make a strong argument for excitation of a diffuse envelope by ultraviolet light from hot stars that have recently formed in the Galactic center. Other mechanisms (relativistic particles, ohmic heating, and shocks) may be present but are energetically unimportant in at least the Sickle region, and by extension probably throughout the Radio Arches as well.
10 citations
TL;DR: In this paper, the MPE/UCB Far Infrared Fabry-Perot Imaging Spectrometer (FIFI) images of galaxies have been made using the FIFI on the KAO with 55" resolution.
8 citations
09 Jun 1994
TL;DR: In this article, visibility data and its analysis for 15 late-type stars observed with the U.C. Berkeley Infrared Spatial Interferometer (ISI) are discussed.
Abstract: We discuss visibility data and its analysis for 15 late-type stars observed with the U. C. Berkeley Infrared Spatial Interferometer (ISI). The ISI is a two-element heterodyne interferometer operating in the 9- to 12-micrometers wavelength region and is located at Mt. Wilson. Visibility curves were calculated using a radiative transfer model and compared with the visibility data from the ISI. A (chi) 2 fitting procedure has been used to estimate the inner radii of the dust shells, optical depths at 11 micrometers , and the temperature at the inner radii. For stars in which the dust is completely resolved estimates of the stellar diameter and temperature can also be made. We present preliminary visibility data for the stars NML Cyg and IRC +10420 obtained recently using a 10-m baseline. In addition, we present preliminary recent data and analysis for the six stars, alpha Ori, omicron Cet, IRC +10216, R Leo, VY CMA, and R Aqr using a 32-m baseline. The visibility data for alpha Ori covers a sufficient range of spatial frequencies to make a determination of its diameter. Within a 95% confidence interval we obtain a diameter of 0".053+/- 0".003. For the other stars the recent 32-m baseline data are compared with previous models and further constrains some of their parameters.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
7 citations
01 Mar 1994
TL;DR: In this article, the authors discuss the implications of recent near-infrared imaging and spectroscopy of the Galactic Center stellar cluster and present two scenarios for the evolution of the central stellar core: one involves a small star formation burst that was the result of substantial prior gas influx into the core.
Abstract: We discuss the implications of recent near-infrared imaging and spectroscopy of the Galactic Center stellar cluster. The central parsec appears to be powered by a cluster of hot, massive stars of which the IRS16 complex is the central core. In the 1 to 2µm band, the brightest members of this cluster are 10 to 15 HeI/HI emission line stars that can be characterized as ≈20,000 K, helium rich, very luminous supergiants. The HeI/HI stars can account for a major fraction of the total and Lyman continuum luminosity of the central parsec, but hotter, earlier type stars are probably required in addition to account for the He-continuum. The brightest cool stars in the central parsec are red supergiants, and asymptotic giant branch stars. We present two scenarios for the evolution of the central stellar core: one involves a small star formation burst a few 106 years ago that was the result of substantial prior gas influx into the core. In this scenario the Galactic Center is presently in a short-lived, post-main sequence “wind phase”. The second scenario involves the buildup of massive stars by sequential merging of lower mass stars. This scenario is plausible if the central stellar density significantly exceeds 107 M⊙ pc-3, as suggested by the surface density distribution on the near-infrared speckle maps. In this case massive star formation may proceed continuously.
4 citations
TL;DR: In this paper, the University of California Infrared Spatial Interferometer (ISI) for the 10 μm wavelength region is briefly described and results obtained on 13 prominent stars and on atmospheric phenomena are discussed.
4 citations
01 Jan 1994
TL;DR: The Garching Conference on the Center of the Galaxy as discussed by the authors has been held in honor of Peter Mezger, and the speakers have covered a wealth of information on the center of our own galaxy and of those nearby.
Abstract: It has been a pleasure and a privilege to attend this conference in honor of Peter Mezger. The speakers have covered a wealth of information on the center of our own galaxy and of those nearby. The sessions have been well planned, informative, and lively. We warmly thank its organizer, Reinhard Genzel, for his scientific leadership and very thoughtful arrangements. We are also indebted to Andy Harris and others members of the Garching staff who have assisted in planning and operation of the conference. We know we have kept Suzanne Harai and Barbara Schnelle very busy with arrangements and with our requests for help, and appreciate their sensitive and efficient management.
4 citations
01 Jan 1994
TL;DR: An overview of the development of molecular astronomy, together with future prospects, is given in this article, together with a review of the current state of the art in molecular astronomy and its future prospects.
Abstract: An overview of the development of molecular astronomy, together with future prospects, is given.
2 citations
TL;DR: Townes as mentioned in this paper has been an active researcher in microwave and infrared spectroscopy for over half a century, and was one of the pioneers in the development of the laser. But this was not the first major meeting of people with backgrounds in both optical and radio imaging, and attracted 200 people from all around the world.
Abstract: This lecture is being given as part of an international meeting on astronomical imaging. It is, in fact, the first major meeting of people with backgrounds in both optical and radio imaging, and has attracted 200 people from all around the world. One of those is a man who has been an active researcher in microwave and infrared spectroscopy for over half a century. It is my pleasure to introduce that man, Professor Charles Townes from the Space Science Laboratory, University of California, Berkeley. It is clear that throughout his life Professor Townes has been attracted by a series of fundamental challenges. He was already an acknowledged molecular spectroscopist when, in 1951, to solve the problem of short wavelength oscillators, he conceived a system for using excited ammonia molecules that became the ammonia beam maser oscillator. He followed this in 1958 by publishing a paper with his brother-in-law, Arthur Schawlow, that laid the foundations for the development of the laser. These two activities, flowing as they did from the pursuit of the most fundamental physics, paved the way for some of the key elements of modern communications.
2 citations
TL;DR: In this paper, velocity resolved maps of the 158 μm [CII] fine structure line, of the 63 μm OI [OI] line, and of the 88 μm and 52μm [OIII] line toward the center region of the Galaxy were reported.
01 Jan 1994
TL;DR: The University of California Infrared Spatial Interferometer (ISI) for the 10 gm wavelength region is briefly described along with results obtained on prominent stars and on atmospheric phenomena as mentioned in this paper.
Abstract: The University of California Infrared Spatial Interferometer (ISI) for the 10 gm wavelength region is briefly described along with results obtained on prominent stars and on atmospheric phenomena. The system has two movable telescopes of 1.65 m aperture. It operates in principle like a modern radio interferometer, using heterodyne detection, CO2 laser local oscillators, RF delay lines, and lobe rotation to maintain a fixed-frequency fringe rate.
01 Jan 1994
TL;DR: In this article, velocity resolved maps of the 158 µm. [CII], the 63 µm [OI], and the 88 µm and 52 µm (OIII) fine structure lines toward the central region of the Galaxy were reported.
Abstract: We report velocity resolved maps of the 158 µm. [CII], the 63 µm [OI], and the 88 µm and 52 µm [OIII] fine structure lines toward the central region of the Galaxy. The angular resolution was 55” for the [CII] line and 22” for the oxygen Unes.
01 Jan 1994
TL;DR: In this article, the Infrared Spatial Interferometer (ISI) has been upgraded with an improved sensitivity, precision and convenience of measurement, and phase fluctuations within the interferometer as well as in the atmosphere above indicate that simple atmospheric models need to be refined.
Abstract: Recent upgrades of the Infrared Spatial Interferometer are described. These provide improved sensitivity, precision and convenience of measurement. Analysis of phase fluctuations within the interferometer as well as in the atmosphere above indicates that popular simple atmospheric models need to be refined. Results of stellar observations are presented in another paper (cf. Danchi et al., in these Proceedings).
01 Jan 1994
TL;DR: In this paper, the spatial distribution of dust around a sample of well-known late-type stars has been studied with the Infrared Spatial Interferometer (ISI) located at Mt. Wilson.
Abstract: The spatial distribution of dust around a sample of well-known late-type stars has been studied with the Infrared Spatial Interferometer (ISI) located at Mt. Wilson. Currently operating with a single baseline as a heterodyne interferometer at 11.15 µm, the ISI has obtained visibility curves of these stars. Radiative transfer modeling of the visibility curves has yielded estimates of the inner radii of the dust shells, the optical depth at 11 µm, and the temperature of the dust at the inner radii. For stars in which the dust is resolved, estimates of the stellar diameter and temperature can also be made. Broadly speaking two classes of stars have been found. One class has inner radii of their dust shells very close to the photospheres of the stars themselves (3-5 stellar radii) and at a higher temperature(~ 1200 K) than previously measured. This class includes VY CMa, NML Tau, IRC +10216, and o Ceti. For the latter two the visibility curves change with the luminosity phase of the star and new dust appears to form at still smaller radii during minimum luminosity. The second class of stars has dust shells with substantially larger inner radii and very little dust close to the stars, and includes α Ori, α Sco, α Her, R Leo, and χ Cyg. This indicates sporadic production of dust and no dust formation within the last several decades.
15 Feb 1994
TL;DR: In this article, the authors compare point-to-point phase fluctuations due to tropospheric and quantum noise, for optimal integration times of 0.2 sec, are approaching the 0.1-cycle level needed to reliably connect the interferometric phase.
Abstract: Infrared interferometric demonstrations with the University of California, Berkeley's infrared spatial interferometer (ISI) on Mt. Wilson explore the potential of infrared and optical astrometry for deep space tracking, reference frame development, and DSN science. Astrometric data taken and analyzed over the last five years from the ISI have shown that instrumental and atmospheric effects limit current demonstrations. The benefits of sensitivity upgrades, which were performed in 1991 and 1992, have been demonstrated by comparing point-to-point phase fluctuations for the fall 1989 and fall 1992 observing epochs. This comparison showed that point-to-point phase fluctuations due to tropospheric and quantum noise, for optimal integration times of 0.2 sec, are approaching the 0.1-cycle level needed to reliably connect the interferometric phase. The increase in sensitivity, coupled with that arising from very recent hardware upgrades, will greatly enhance phase-connection capabilities necessary for astrometry in the presence of atmospheric refractivity fluctuations. The current data set suggests that atmospheric fluctuations on Mt. Wilson during the best seeing are dominated by a low-lying component, approximately 25 m high, which may be minimized with in situ calibration in the future. During poor seeing conditions that currently prohibit the interferometric phase connection necessary for astrometry, fluctuations seem to be generated by atmospheric inhomogeneities at much higher altitudes above Mt. Wilson. Data taken over the last year suggest that the ISI will soon be able to achieve 50- to 100-nrad astrometry in a single observing session, employing current ground-based laser distance interferometer calibrations to minimize atmospheric effects.
09 Jun 1994
TL;DR: In this article, the U.C. Berkeley Infrared Spatial Interferometer (ISI) on Mt. Wilson was used to demonstrate a 10-milliarcsecond (mas) capability for tracking stellar and solar system objects.
Abstract: Infrared astrometry at the 10-milliarcsecond (mas) level is applicable to experiments in stellar evolution astronomy, solar system dynamics, relativistic gravitation, and deep space laser tracking. We are pursing astrometry with the U. C. Berkeley Infrared Spatial Interferometer (ISI) on Mt. Wilson to demonstrate a 10-mas capability for tracking stellar and solar system objects. Astrometric data from the ISI, taken and analyzed over the last 5 years, have shown that instrumental and atmospheric effects limit current demonstrations. The ISI data show that point-to-point interferometric phase fluctuations due to tropospheric and quantum noise, for optimal integration times of 0.2 seconds, are approaching the 0.1-cycle level needed to reliably connect the phase. Modeling the ISI data suggests that atmospheric fluctuations on Mt. Wilson, during the best seeing, are dominated by a low-lying component, within the first 25 meters above the ISI, which, in the future, may be minimized with in situ calibration. A calculation of atmosphere-limited astrometric accuracy shows that the ISI will soon be able to achieve 10-mas astrometry, on a 13-m baseline in a single observing session, employing current ground-based laser distance interferometer calibrations to minimize atmospheric effects.
01 Jan 1994
TL;DR: In this paper, the Infrared Spatial Interferometer (ISI) has been upgraded with an improved sensitivity, precision and convenience of measurement, and phase fluctuations within the interferometer as well as in the atmosphere above indicate that simple atmospheric models need to be refined.
Abstract: Recent upgrades of the Infrared Spatial Interferometer are described. These provide improved sensitivity, precision and convenience of measurement. Analysis of phase fluctuations within the interferometer as well as in the atmosphere above indicates that popular simple atmospheric models need to be refined. Results of stellar observations are presented in another paper (cf. Danchi et al., in these Proceedings).