At sufficiently low frequencies, no ground-based radio array will be able to produce high resolut... more At sufficiently low frequencies, no ground-based radio array will be able to produce high resolution images while looking through the ionosphere. A space-based array will be needed to explore the objects and processes which dominate the sky at the lowest radio frequencies. An imaging radio interferometer based on a large number of small, inexpensive satellites would be able to track solar radio bursts associated with coronal mass ejections out to the distance of Earth, determine the frequency and duration of early epochs of nonthermal activity in galaxies, and provide unique information about the interstellar medium. This would be a "spacespace" VLBI mission, as only baselines between satellites would be used. Angular resolution would be limited only by interstellar and interplanetary scattering.
Isolated type III radio bursts activity was observed at Clark Lake Radio Observatory in March and... more Isolated type III radio bursts activity was observed at Clark Lake Radio Observatory in March and the first part of April 1971 to occur in discrete regions of the corona above certain active regions. When these regions were examined under high resolution in H alpha all the type III events appeared to have associated activity in H alpha. The potential coronal magnetic field in these regions appeared to be either open or diverging, whereas the field over a rather active region which did not have radio burst activity was closed in a magnetic arcade. The latter feature has been associated with streamers. Streamers have also been associated with dark filaments. The occurrence of a stable dark filament in an active region appeared to have an inhibiting effect on type III activity. It is suggested that a streamer field configuration is not favorable to the escape of isolated type III exciters.
Scheduled among the deep space communications activities of the '70-m antennas of the NASA Deep S... more Scheduled among the deep space communications activities of the '70-m antennas of the NASA Deep Space Network (DSN) are diverse astronomical observing programs with different requirements. For example, the US Space VLBI Project puts great emphasis on reliability for a few well-defined types of observations, for which the software is essentially frozen for the duration of the Project. On the other hand, Solar System Radar research and observations of regions of star formation need ongoing development, sometimes in real-time, of data acquisition and monitor and control software. This paper describes the methodology by which we can allow each user or project a high degree of customization. To do this we rely on a mixture of public domain software (e.g. Perl, Tcl, Tk, PGPLOT) and locally developed software. The scheme allows the software configuration in the Radio Astronomy Controller to be switched to an observer's or project's specific configuration within minutes, including specific releases of public domain software. At the core of the Radio Astronomy Controller is a server that controls the R&D equipment. The behavior of this server is largely determined by Tcl scripts, which are customized €or the observer or project. An observer working interactively can use a customized Tk client to direct the server via TCP, as well as DSN operational (non-R&D) equipment via another server which CommuniLates with DSN controllers. A project or user may alternatively run a client which is specialized for unattended operations.
We have carried out deep search for radio emission at 150 MHz from the extra-solar planet system ... more We have carried out deep search for radio emission at 150 MHz from the extra-solar planet system Upsilon Andromedae using the Giant Meter Wave Radio Telescope (GMRT). Estimates using conservative scaling laws based on the five radio planets in our Solar system indicate an expected flux density of approximately 150 mJy at 150 MHz for the "Hot Jupiter" in the Upsilon Andromeda system. However the two epoch observation of this system with GMRT at 150 MHz yielded a 3 sigma upper limit of 2.5 mJy for the average flux. We also present the light-curve analysis for detecting bursts of emission, if any.
Water maser emission at 22 GHz, resolvable in position and velocity, provides a unique probe of t... more Water maser emission at 22 GHz, resolvable in position and velocity, provides a unique probe of the geometry and dynamics of the central parsec of highly obscured AGN. While only ~5% of narrow line AGN host water masers, this rarity is a clue to the physical processes in these AGN. We will present studies which show a link between maser emission and the obscuration, [OIII] luminosity (i.e. bolometric luminosity), and velocity dispersion (i.e. mass) of AGN. In addition, the narrow range in the temperature and density requirements for maser emission provide localized measurements of the temperature and density profiles within the parsec scale disks, enabling us to test theories on accretion and obscuration.
The increasing load on NASA's deep Space Network, the new capabilities for deep space mission... more The increasing load on NASA's deep Space Network, the new capabilities for deep space missions inherent in a next-generation radio telescope, and the potential of new telescope technology for reducing construction and operation costs suggest a natural marriage between radio astronomy and deep space telecommunications in developing advanced radio telescope concepts.
The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented... more The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented. Measurements were done between March and July 1989 using Virgo A and Venus as the primary efficiency calibrators. The flux densites of theses radio sources at 32 GHz are not known with high accuracy, but were extrapolated from calibrated data at lower frequencies. The measured value of efficiency (0.35) agreed closely with the predicted value (0.32), and the results are very repeatable. Flux densities of secondary sources used in the observations were subsequently derived. These measurements were performed using a beamswitching radiometer that employed an uncooled high-electron mobility transistor (HEMT) low-noise amplifier. This system was installed primarily to determine the performance of the antenna in its 1989 configuration, but the experience will also aid in successful future calibration of the Deep Space Network (DSN) at this frequency.
We present a method for deriving the electron density of ionized gas using the ratio of the inten... more We present a method for deriving the electron density of ionized gas using the ratio of the intensity of the [N II] 205 μm line to that of hydrogen radio recombination lines (RRLs). We use this method to derive electron densities of 21 velocity components in 11 lines of sight through the Galaxy, including the Galactic center. We observed, at high spectral resolution, the [N II] 205 μm with the Herschel/HIFI and SOFIA/GREAT instruments and the RRLs with the Green Bank Telescope and the NASA Deep Space Network Deep Space Station 43 (DSS-43) telescope. We find typical electron densities between 8 and 170 cm −3 , which are consistent with those derived at low spectral resolution using the [N II] 205 μm/122 μm ratio with Herschel/PACS on a larger sample of sight lines in the Galactic plane. By matching the electron densities derived from the [N II] 205 μm/RRL intensity ratio and the [N II] 122 μm/205 μm intensity ratio, we derive the nitrogen fractional abundance for most of the velocity components. We investigate the dependence of the N/H ratio on galactocentric distance in the inner Galaxy (R gal <6 kpc), which is inaccessible in optical studies owing to dust extinction. We find that the distribution of nitrogen abundances in the inner Galaxy derived from our data has a slope that is consistent with that found in the outer Galaxy in optical studies. This result is inconsistent with some suggestions of a flatter distribution of the nitrogen abundance in the inner Galaxy.
We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Te... more We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Terahertz Observatory 2 (STO2). The Trumpler 14/Carina I region is in the west part of the Carina Nebula Complex, which is one of the most extreme star-forming regions in the Milky Way. We observed Trumpler 14/Carina I in the 158 µm transition of [C ii] with a spatial resolution of 48 and a velocity resolution of 0.17 km s −1. The observations cover a 0.25 • by 0.28 • area with central position l = 297.34 • , b =-0.60 •. The kinematics show that bright [C ii] structures are spatially and spectrally correlated with the surfaces of CO clouds, tracing the photodissociation region and ionization front of each molecular cloud. Along 7 lines of sight that traverse Tr 14 into the dark ridge to the southwest, we find that the [C ii] luminosity from the HII region is 3.7 times that from the PDR. In same los we find in the PDRs an average ratio of 1:4.1:5.6 for the mass in atomic gas:dark-CO gas: molecular gas traced by CO. Comparing multiple gas tracers including HI 21cm, [C ii], CO, and radio recombination lines, we find that the HII regions of the Carina Nebula Complex are well-described as HII regions with one-side freely expanding towards us, consistent with the champagne model of ionized gas evolution. The dispersal of the GMC in this region is dominated by EUV photoevaporation; the dispersal timescale is 20-30 Myr.
We report the most sensitive water maser survey towards Bok globules to date, using NASA's 70m an... more We report the most sensitive water maser survey towards Bok globules to date, using NASA's 70m antenna in Robledo de Chavela (Spain). We observed 207 positions within the Clemens & Barvainis (1988) catalog with a higher probability of harboring a young star, using as selection criteria the presence of radio continuum emission (from submillimeter to centimeter wavelengths), geometrical centers of molecular outflows, peaks in maps of high-density gas tracers (NH 3 or CS), and IRAS point sources. We have obtained 7 maser detections, 6 of which (in CB 34, CB 54, CB 65, CB 101, CB 199, and CB 232) are reported for the first time here. Most of the water masers we detected are likely to be associated with young stellar objects (YSOs), except for CB 101 (probably an evolved object) and CB 65 (uncertain nature). The water maser in CB 199 shows a relatively high shift (≃ 30 km s −1) of its velocity centroid with respect to the cloud velocity, which is unusual for low-mass YSOs. We speculate that high-velocity masers in this kind of object could be related with episodes of energetic mass-loss in close binaries. Alternatively, the maser in CB 199 could be pumped by a protoplanetary or a young planetary nebula. CB 232 is the smallest Bok globule (≃ 0.6 pc) known to be associated with water maser emission, although it would be superseded by the cases of CB 65 (≃ 0.3 pc) and CB 199 (≃ 0.5 pc) if their association with YSOs is confirmed. All our selection criteria have statistically compatible detection rates, except for IRAS sources, which tend to be a somewhat worse predictor for the presence of maser emission.
At sufficiently low frequencies, no ground-based radio array will be able to produce high resolut... more At sufficiently low frequencies, no ground-based radio array will be able to produce high resolution images while looking through the ionosphere. A space-based array will be needed to explore the objects and processes which dominate the sky at the lowest radio frequencies. An imaging radio interferometer based on a large number of small, inexpensive satellites would be able to track solar radio bursts associated with coronal mass ejections out to the distance of Earth, determine the frequency and duration of early epochs of nonthermal activity in galaxies, and provide unique information about the interstellar medium. This would be a "spacespace" VLBI mission, as only baselines between satellites would be used. Angular resolution would be limited only by interstellar and interplanetary scattering.
Isolated type III radio bursts activity was observed at Clark Lake Radio Observatory in March and... more Isolated type III radio bursts activity was observed at Clark Lake Radio Observatory in March and the first part of April 1971 to occur in discrete regions of the corona above certain active regions. When these regions were examined under high resolution in H alpha all the type III events appeared to have associated activity in H alpha. The potential coronal magnetic field in these regions appeared to be either open or diverging, whereas the field over a rather active region which did not have radio burst activity was closed in a magnetic arcade. The latter feature has been associated with streamers. Streamers have also been associated with dark filaments. The occurrence of a stable dark filament in an active region appeared to have an inhibiting effect on type III activity. It is suggested that a streamer field configuration is not favorable to the escape of isolated type III exciters.
Scheduled among the deep space communications activities of the '70-m antennas of the NASA Deep S... more Scheduled among the deep space communications activities of the '70-m antennas of the NASA Deep Space Network (DSN) are diverse astronomical observing programs with different requirements. For example, the US Space VLBI Project puts great emphasis on reliability for a few well-defined types of observations, for which the software is essentially frozen for the duration of the Project. On the other hand, Solar System Radar research and observations of regions of star formation need ongoing development, sometimes in real-time, of data acquisition and monitor and control software. This paper describes the methodology by which we can allow each user or project a high degree of customization. To do this we rely on a mixture of public domain software (e.g. Perl, Tcl, Tk, PGPLOT) and locally developed software. The scheme allows the software configuration in the Radio Astronomy Controller to be switched to an observer's or project's specific configuration within minutes, including specific releases of public domain software. At the core of the Radio Astronomy Controller is a server that controls the R&D equipment. The behavior of this server is largely determined by Tcl scripts, which are customized €or the observer or project. An observer working interactively can use a customized Tk client to direct the server via TCP, as well as DSN operational (non-R&D) equipment via another server which CommuniLates with DSN controllers. A project or user may alternatively run a client which is specialized for unattended operations.
We have carried out deep search for radio emission at 150 MHz from the extra-solar planet system ... more We have carried out deep search for radio emission at 150 MHz from the extra-solar planet system Upsilon Andromedae using the Giant Meter Wave Radio Telescope (GMRT). Estimates using conservative scaling laws based on the five radio planets in our Solar system indicate an expected flux density of approximately 150 mJy at 150 MHz for the "Hot Jupiter" in the Upsilon Andromeda system. However the two epoch observation of this system with GMRT at 150 MHz yielded a 3 sigma upper limit of 2.5 mJy for the average flux. We also present the light-curve analysis for detecting bursts of emission, if any.
Water maser emission at 22 GHz, resolvable in position and velocity, provides a unique probe of t... more Water maser emission at 22 GHz, resolvable in position and velocity, provides a unique probe of the geometry and dynamics of the central parsec of highly obscured AGN. While only ~5% of narrow line AGN host water masers, this rarity is a clue to the physical processes in these AGN. We will present studies which show a link between maser emission and the obscuration, [OIII] luminosity (i.e. bolometric luminosity), and velocity dispersion (i.e. mass) of AGN. In addition, the narrow range in the temperature and density requirements for maser emission provide localized measurements of the temperature and density profiles within the parsec scale disks, enabling us to test theories on accretion and obscuration.
The increasing load on NASA's deep Space Network, the new capabilities for deep space mission... more The increasing load on NASA's deep Space Network, the new capabilities for deep space missions inherent in a next-generation radio telescope, and the potential of new telescope technology for reducing construction and operation costs suggest a natural marriage between radio astronomy and deep space telecommunications in developing advanced radio telescope concepts.
The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented... more The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented. Measurements were done between March and July 1989 using Virgo A and Venus as the primary efficiency calibrators. The flux densites of theses radio sources at 32 GHz are not known with high accuracy, but were extrapolated from calibrated data at lower frequencies. The measured value of efficiency (0.35) agreed closely with the predicted value (0.32), and the results are very repeatable. Flux densities of secondary sources used in the observations were subsequently derived. These measurements were performed using a beamswitching radiometer that employed an uncooled high-electron mobility transistor (HEMT) low-noise amplifier. This system was installed primarily to determine the performance of the antenna in its 1989 configuration, but the experience will also aid in successful future calibration of the Deep Space Network (DSN) at this frequency.
We present a method for deriving the electron density of ionized gas using the ratio of the inten... more We present a method for deriving the electron density of ionized gas using the ratio of the intensity of the [N II] 205 μm line to that of hydrogen radio recombination lines (RRLs). We use this method to derive electron densities of 21 velocity components in 11 lines of sight through the Galaxy, including the Galactic center. We observed, at high spectral resolution, the [N II] 205 μm with the Herschel/HIFI and SOFIA/GREAT instruments and the RRLs with the Green Bank Telescope and the NASA Deep Space Network Deep Space Station 43 (DSS-43) telescope. We find typical electron densities between 8 and 170 cm −3 , which are consistent with those derived at low spectral resolution using the [N II] 205 μm/122 μm ratio with Herschel/PACS on a larger sample of sight lines in the Galactic plane. By matching the electron densities derived from the [N II] 205 μm/RRL intensity ratio and the [N II] 122 μm/205 μm intensity ratio, we derive the nitrogen fractional abundance for most of the velocity components. We investigate the dependence of the N/H ratio on galactocentric distance in the inner Galaxy (R gal <6 kpc), which is inaccessible in optical studies owing to dust extinction. We find that the distribution of nitrogen abundances in the inner Galaxy derived from our data has a slope that is consistent with that found in the outer Galaxy in optical studies. This result is inconsistent with some suggestions of a flatter distribution of the nitrogen abundance in the inner Galaxy.
We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Te... more We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Terahertz Observatory 2 (STO2). The Trumpler 14/Carina I region is in the west part of the Carina Nebula Complex, which is one of the most extreme star-forming regions in the Milky Way. We observed Trumpler 14/Carina I in the 158 µm transition of [C ii] with a spatial resolution of 48 and a velocity resolution of 0.17 km s −1. The observations cover a 0.25 • by 0.28 • area with central position l = 297.34 • , b =-0.60 •. The kinematics show that bright [C ii] structures are spatially and spectrally correlated with the surfaces of CO clouds, tracing the photodissociation region and ionization front of each molecular cloud. Along 7 lines of sight that traverse Tr 14 into the dark ridge to the southwest, we find that the [C ii] luminosity from the HII region is 3.7 times that from the PDR. In same los we find in the PDRs an average ratio of 1:4.1:5.6 for the mass in atomic gas:dark-CO gas: molecular gas traced by CO. Comparing multiple gas tracers including HI 21cm, [C ii], CO, and radio recombination lines, we find that the HII regions of the Carina Nebula Complex are well-described as HII regions with one-side freely expanding towards us, consistent with the champagne model of ionized gas evolution. The dispersal of the GMC in this region is dominated by EUV photoevaporation; the dispersal timescale is 20-30 Myr.
We report the most sensitive water maser survey towards Bok globules to date, using NASA's 70m an... more We report the most sensitive water maser survey towards Bok globules to date, using NASA's 70m antenna in Robledo de Chavela (Spain). We observed 207 positions within the Clemens & Barvainis (1988) catalog with a higher probability of harboring a young star, using as selection criteria the presence of radio continuum emission (from submillimeter to centimeter wavelengths), geometrical centers of molecular outflows, peaks in maps of high-density gas tracers (NH 3 or CS), and IRAS point sources. We have obtained 7 maser detections, 6 of which (in CB 34, CB 54, CB 65, CB 101, CB 199, and CB 232) are reported for the first time here. Most of the water masers we detected are likely to be associated with young stellar objects (YSOs), except for CB 101 (probably an evolved object) and CB 65 (uncertain nature). The water maser in CB 199 shows a relatively high shift (≃ 30 km s −1) of its velocity centroid with respect to the cloud velocity, which is unusual for low-mass YSOs. We speculate that high-velocity masers in this kind of object could be related with episodes of energetic mass-loss in close binaries. Alternatively, the maser in CB 199 could be pumped by a protoplanetary or a young planetary nebula. CB 232 is the smallest Bok globule (≃ 0.6 pc) known to be associated with water maser emission, although it would be superseded by the cases of CB 65 (≃ 0.3 pc) and CB 199 (≃ 0.5 pc) if their association with YSOs is confirmed. All our selection criteria have statistically compatible detection rates, except for IRAS sources, which tend to be a somewhat worse predictor for the presence of maser emission.
Uploads
Papers by Tom Kuiper