Christopher L. Martin

SIMULTANEOUS MULTI-WAVELENGTH OBSERVATIONS OF Sgr A* DURING 2007 APRIL 1-11

We report the detection of variable emission from Sgr A* in almost all wavelength bands (i.e., centimeter, millimeter, submillimeter, near-IR, and X-rays) during a multi-wavelength observing campaign. Three new moderate flares are detected simultaneously in both near-IR and X-ray bands. The ratio of X-ray to near-IR flux in the flares is consistent with inverse Compton scattering of near-IR photons by submillimeter emitting relativistic particles which follow scaling relations obtained from size measurements of Sgr A*. We also find that the flare statistics in near-IR wavelengths is consistent with the probability of flare emission being inversely proportional to the flux. At millimeter wavelengths, the presence of flare emission at 43 GHz (7 mm) using the Very Long Baseline Array with milliarcsecond spatial resolution indicates the first direct evidence that hourly timescale flares are localized within the inner 30 × 70 Schwarzschild radii of Sgr A*. We also show several cross-correlation plots between near-IR, millimeter, and submillimeter light curves that collectively demonstrate the presence of time delays between the peaks of emission up to 5 hr. The evidence for time delays at millimeter and submillimeter wavelengths are consistent with the source of emission initially being optically thick followed by a transition to an optically thin regime. In particular, there is an intriguing correlation between the optically thin near-IR and X-ray flare and optically thick radio flare at 43 GHz that occurred on 2007 April 4. This would be the first evidence of a radio flare emission at 43 GHz delayed with respect to the near-IR and X-ray flare emission. The time delay measurements support the expansion of hot self-absorbed synchrotron plasma blob and weaken the hot spot model of flare emission. In addition, a simultaneous fit to 43 and 84 GHz light curves, using an adiabatic expansion model of hot plasma, appears to support a power law rather than a relativistic Maxwellian distribution of particles.

Trapping of dextran-coated colloids in liposomes by transient binding to aminophospholipid: preparation of ferrosomes

A procedure is described that allows to increase the efficiency of the loading of liposomes with dextran-stabilized iron oxides (MION). The method produces a preparation of liposomes (REVs) with high iron oxide content as a result of transient binding of oxidized dextran with amino groups of aminophospholipids. Phosphatidylethanolamine (PE)-containing lipid mixtures (PC/DOPE/CH or SM/DOPE/CH, 9:2:9 molar ratio) in organic phase were combined with oxidized MION at pH 8. Liposomes then were obtained by reversed-phase evaporation. Liposomes, 263 +/- 89 nm in diameter, contained up to 11.8 mol Fe/mol phospholipid (encapsulation yield 49%). 10.2% of liposome-associated iron was dissociated from liposomes upon changing the pH to 4.5. When lipid compositions of extracts prepared from liposomes incubated at pH 4.5 and pH 8.0 were compared, an increase of relative PE-content in extracts of liposomes incubated at lowered pH was detected. This indicates a dissociation of imine bonds between aldehydes on the MION surface and PE. The accessibility of liposomal PE for acylation was demonstrated by modification with an activated ester of methoxy poly(ethylene glycol) succinate. Control liposomes, containing no aminophospholipid, or PE-containing liposomes obtained in the presence of non-oxidized MION, were 3.5-5-fold less effective for MION encapsulation and showed extensive aggregation.

The AST/RO Survey of the Galactic Center Region. I. The Inner 3 Degrees

We present fully-sampled maps of 461 GHz CO (4-3), 807 GHz CO (7-6), and 492 GHz [CI] (3P1-3P0) emission from the inner 3 degrees of the Galactic Center region taken with the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) in 2001--2002. The data cover -1.3 70K) at cloud edges to low values (<50K) in the interiors. Typical gas pressures in the Galactic Center gas are n(H_2) T_kin approx 10^5.2 K cm^-3. We also present an (l,b) map of molecular hydrogen column density derived from our LVG results.

The Mopra southern Galactic plane CO survey

We present the first results from a new carbon monoxide (CO) survey of the southern Galactic plane being conducted with the Mopra radio telescope in Australia. The 12 CO, 13 CO, and C 18 O J = 1‐0 lines are being mapped over the l = 305 ◦ ‐345 ◦ ,b =± 0.5 ◦ portion of the fourth quadrant of the Galaxy, at 35 arcsec spatial and 0.1 km s −1 spectral resolution. The survey is being undertaken with two principal science objectives: (i) to determine where and how molecular clouds are forming in the Galaxy and (ii) to probe the connection between molecular clouds and the ‘missing’ gas inferred from gamma-ray observations. We describe the motivation for the survey, the instrumentation and observing techniques being applied, and the data reduction and analysis methodology. In this paper, we present the data from thefirst degree surveyed, l = 323 ◦ ‐324 ◦ ,b =± 0.5 ◦ . We compare the data to the previous CO survey of this region and present metrics quantifying the performance being achieved; the rms sensitivity per 0.1 km s −1 velocity channel is 1.5 K for 12 CO and 0.7 K for the other lines. We also present some results from the region surveyed, including line fluxes, column densities, molecular masses, 12 CO/ 13 CO line ratios, and 12 CO optical depths. We also examine how these quantities vary as a function of distance from the Sun when averaged over the 1 square degree survey area. Approximately 2 × 10 6 M� of molecular gas is found along the G323 sightline, with an average H2 number density of nH 2 ∼ 1c m −3 within the Solar

Gas Density, Stability, and Starbursts near the Inner Lindblad Resonance of the Milky Way

A key project of the Antarctic Submillimeter Telescope and Remote Observatory reported by Martin et al. is the mapping of CO J = 4 → 3 and J = 7 → 6 emission from the inner Milky Way, allowing determination of gas density and temperature. Galactic center gas that Binney et al. identify as being on x2 orbits has a density near 103.5 cm-3, which renders it only marginally stable against gravitational coagulation into a few giant molecular clouds, as discussed by Elmegreen. This suggests a relaxation oscillator mechanism for starbursts in the Milky Way, whereby inflowing gas accumulates in a ring at 150 pc radius until the critical density is reached and the resulting instability leads to the sudden formation of giant clouds and the deposition of 4 × 107 M☉ of gas onto the Galactic center. Depending on the accretion rate near the inner Lindblad resonance, this cycle will repeat with a timescale of order 20 Myr.

ANTARCTIC SUBMILLIMETER TELESCOPE AND REMOTE OBSERVATORY OBSERVATIONS OF CO J =7 !6 AND J =4 !3 EMISSION TOWARD THE GALACTIC CENTER REGION

We present position-velocity strip maps of the Galactic center region in the CO J ¼ 7 ! 6a ndJ ¼ 4 ! 3 transitions observed with the Antarctic Submillimeter Telescope and Remote Observatory located at the Amundsen-Scott South Pole Station. Emission from the two rotational transitions of 12 CO was mapped at b ¼ 0 � for 3=5 > l > � 1= 5o n a1 0 grid with a FWHM beam size of 58 00 at 806 GHz and 105 00 at 461 GHz. Previous observations of CO J ¼ 4 ! 3 (C. L. Martin et al., in preparation) and of [C i] emission (Ojha et al.) from this region show that these lines are distributed in a manner similar to CO J ¼ 1 ! 0 (Stark et al.); the (CO J ¼ 4 ! 3)/(CO J ¼ 1 ! 0) line ratio map is almost featureless across the entire Galactic center region. In contrast, the CO J ¼ 7 ! 6 emission from the Galactic center is strongly peaked toward the Sgr A and Sgr B molecular complexes. A large velocity gradient analysis shows that, aside from the two special regions Sgr A and Sgr B, the photon-dominated regions within a few hundred parsecs of the Galactic center are remarkably uniform in mean density and kinetic temperature at n ¼ 2500–4000 cm � 3 and T ¼ 30–45 K. The (CO J ¼ 7 ! 6)/(CO J ¼ 4 ! 3) line temperature ratios near Sgr B are a factor of 2 higher than those observed in the nuclear region of the starburst galaxy M82 (Mao et al.), while the CO(J ¼ 7 ! 6)/ CO(J ¼ 4 ! 3) line temperature ratios around Sgr A are similar to M82. The line ratio on large scales from the Galactic center region is an order of magnitude less than that from M82. Subject headings: Galaxy: abundances — Galaxy: center — ISM: general — ISM: molecules — submillimeter

Pre-HEAT: submillimeter site testing and astronomical spectra from Dome A, Antarctica

Pre-HEAT is a 20 cm aperture submillimeter-wave telescope with a 660 GHz (450 micron) Schottky diode heterodyne receiver and digital FFT spectrometer for the Plateau Observatory (PLATO) developed by the University of New South Wales. In January 2008 it was deployed to Dome A, the summit of the Antarctic plateau, as part of a scientific traverse led by the Polar Research Institute of China and the Chinese Academy of Sciences. Dome A may be one of the best sites in the world for ground based Terahertz astronomy, based on the exceptionally cold, dry and stable conditions which prevail there. Pre-HEAT is measuring the 450 micron sky opacity at Dome A and mapping the Galactic Plane in the 13CO J=6-5 line, constituting the first submillimeter measurements from Dome A. It is field-testing many of the key technologies for its namesake -- a successor mission called HEAT: the High Elevation Antarctic Terahertz telescope. Exciting prospects for submillimeter astronomy from Dome A and the status of Pre-HEAT will be presented.

Millimeter and Submillimeter Survey of the R Coronae Australis Region

Using a combination of data from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), the Arizona Radio Observatory Kitt Peak 12 m telescope, and the Arizona Radio Observatory 10 m Heinrich Hertz Telescope, we have studied the most active part of the R CrA molecular cloud in multiple transitions of carbon monoxide, HCO+, and 870 μm continuum emission. Since R CrA is nearby (130 pc), we are able to obtain physical spatial resolution as high as 0.01 pc over an area of 0.16 pc2, with velocity resolution finer than 1 km s-1. Mass estimates of the protostar driving the millimeter-wave emission derived from HCO+, dust continuum emission, and kinematic techniques point to a young, deeply embedded protostar of ~0.5-0.75 M☉, with a gaseous envelope of similar mass. A molecular outflow is driven by this source that also contains at least 0.8 M☉ of molecular gas with ~0.5 L☉ of mechanical luminosity. HCO+ lines show the kinematic signature of infall motions, as well as bulk rotation. The source is most likely a Class 0 protostellar object not yet visible at near-IR wavelengths. With the combination of spatial and spectral resolution in our data set, we are able to disentangle the effects of infall, rotation, and outflow toward this young object.

The Stratospheric THz Observatory (STO)

The Stratospheric TeraHertz Observatory (STO) is a NASA funded, Long Duration Balloon (LDB) experiment designed to address a key problem in modern astrophysics: understanding the Life Cycle of the Interstellar Medium (ISM). STO will survey a section of the Galactic plane in the dominant interstellar cooling line [C II] (1.9 THz) and the important star formation tracer [N II] (1.46 THz) at ~1 arc minute angular resolution, sufficient to spatially resolve atomic, ionic and molecular clouds at 10 kpc. STO itself has three main components; 1) an 80 cm optical telescope, 2) a THz instrument package, and 3) a gondola [1]. Both the telescope and gondola have flown on previous experiments [2,3]. They have been reoptimized for the current mission. The science flight receiver package will contain four [CII] and four [NII] HEB mixers, coupled to a digital spectrometer. The first engineering test flight of STO was from Ft. Sumner, NM on October 15, 2009. The ~30 day science flight is scheduled for December 2011.

13C I in high-mass star-forming clouds

We report measurements of the 12C/13C abundance ratio in the three galactic regions G 333.0-0.4, NGC 6334 A and G 351.6-1.3 from observations of the 12CI 3P2-3P1 transition and the hyperfine components of the corresponding 13CI transition near 809 GHz. These transitions were observed simultaneously with the CO 7-6 line emission at 806 GHz with the AST/RO telescope located at the South Pole. From a simultaneous fit to the 12CI 3P2-3P1 transition and the HF components of the corresponding 13CI transition and an independent estimate of an upper limit to the optical depth of the 12CI emission we determine intrinsic 12CI/13CI column density ratios of 23+-1 for G 333.0-0.4, 56+-14 for NGC 6334 A and 69+-12 for G 351.6-1.3. As the regions observed are photon dominated, we argue that the apparent enhancement in the abundance of 13C towards G 333.0-0.4 may be due to strong isotope-selective photodissociation of 13CO, outweighing the effects of chemical isotopic fractionation as suggested by models of PDRs. Towards NGC 6334 A and G 351.6-1.3 these effects appear to be balanced, similar to the situation for the Orion Bar region observed by Keene et al. (1998).