| 1. |
|
|
| 2. |
|
|
| 3. |
- Ginsburg, A., et al.
(författare)
-
Dense gas in the Galactic central molecular zone is warm and heated by turbulence
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 586, s. Art nr A50-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The Galactic center is the closest region where we can study star formation under extreme physical conditions like those in high-redshift galaxies. Aims. We measure the temperature of the dense gas in the central molecular zone (CMZ) and examine what drives it. Methods. We mapped the inner 300 pc of the CMZ in the temperature-sensitive J = 3-2 para-formaldehyde (p-H2CO) transitions. We used the 3(2,1)-2(2,0)/3(0,3)-2(0,2) line ratio to determine the gas temperature in n similar to 10(4) - 10(5) cm(-3) gas. We have produced temperature maps and cubes with 30 0 0 and 1 km s(-1) resolution and published all data in FITS form. Results. Dense gas temperatures in the Galactic center range from similar to 60 K to > 100 K in selected regions. The highest gas temperatures T-G > 100 K are observed around the Sgr B2 cores, in the extended Sgr B2 cloud, the 20 km s(-1) and 50 km s(-1) clouds, and in "The Brick" (G0.253 + 0.016). We infer an upper limit on the cosmic ray ionization rate zeta(CR)
|
|
| 4. |
- Belitsky, Victor, 1955, et al.
(författare)
-
SEPIA - A new single pixel receiver at the APEX telescope
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
-
Tidskriftsartikel (refereegranskat)abstract
- Context. We describe the new Swedish-ESO PI Instrument for APEX (SEPIA) receiver, which was designed and built by the Group for Advanced Receiver Development (GARD), at Onsala Space Observatory (OSO) in collaboration with ESO. It was installed and commissioned at the APEX telescope during 2015 with an ALMA Band 5 receiver channel and updated with a new frequency channel (ALMA Band 9) in February 2016. Aim. This manuscript aims to provide, for observers who use the SEPIA receiver, a reference in terms of the hardware description, optics and performance as well as the commissioning results. Methods. Out of three available receiver cartridge positions in SEPIA, the two current frequency channels, corresponding to ALMA Band 5, the RF band 158-211 GHz, and Band 9, the RF band 600-722 GHz, provide state-of-the-art dual polarization receivers. The Band 5 frequency channel uses 2SB SIS mixers with an average SSB noise temperature around 45 K with IF (intermediate frequency) band 4-8 GHz for each sideband providing total 4 × 4 GHz IF band. The Band 9 frequency channel uses DSB SIS mixers with a noise temperature of 75-125 K with IF band 4-12 GHz for each polarization. Results. Both current SEPIA receiver channels are available to all APEX observers.
|
|
| 5. |
- Galametz, M., et al.
(författare)
-
Water, methanol and dense gas tracers in the local ULIRG Arp 220: results from the new SEPIA Band 5 Science Verification campaign
- 2016
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 462:1, s. L36-L40
-
Tidskriftsartikel (refereegranskat)abstract
- We present a line survey of the ultraluminous infrared galaxy Arp 220, taken with the newly installed SEPIA (Swedish-European Southern Observatory PI receiver for APEX) Band 5 instrument on APEX (Atacama Pathfinder Experiment). We illustrate the capacity of SEPIA to detect the 183.3 GHz H(2)O3(1,3)-2(2,0) line against the atmospheric H2O absorption feature. We confirm the previous detection of the HCN(2-1) line, and detect new transitions of standard dense gas tracers such as HNC(2-1), HCO+(2-1), CS(4-3), (CS)-S-34(4-3) and HC3N(20-19). We also detect HCN(2-1) v(2) = 1 and the 193.5 GHz methanol (4-3) group for the first time. The absence of time variations in the megamaser water line compared to previous observations seems to rule out an AGN nuclear origin for the line. It could, on the contrary, favour a thermal origin instead, but also possibly be a sign that the megamaser emission is associated with star-forming cores washed out in the beam. We finally discuss how the new transitions of HCN, HNC and HCO+ refine our knowledge of the interstellar medium physical conditions in Arp 220.
|
|
| 6. |
- Humphreys, E. M., et al.
(författare)
-
Simultaneous 183 GHz H2O maser and SiO observations towards evolved stars using APEX SEPIA Band 5
- 2017
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 603, s. A77-
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim is to investigate the use of 183 GHz H2O masers for characterization of the physical conditions and mass loss process in the circumstellar envelopes of evolved stars. Methods. We used APEX SEPIA Band 5 (an ALMA Band 5 receiver on the APEX telescope) to observe the 183 GHz H2O line towards two red supergiant (RSG) and three asymptotic giant branch (AGB) stars. Simultaneously, we observed the J = 4-3 line for (SiO)-Si-28 nu = 0, 1, 2 and 3, and for (SiO)-Si-29 nu = 0 and 1. We compared the results with simulations and radiative transfer models for H2O and SiO, and examined data for the individual linear orthogonal polarizations. Results. We detected the 183 GHz H2O line towards all the stars with peak flux densities >100 Jy, including a new detection from VYCMa. Towards all five targets, the water line had indications of being caused by maser emission and had higher peak flux densities than for the SiO lines. The SiO lines appear to originate from both thermal and maser processes. Comparison with simulations and models indicate that 183 GHz maser emission is likely to extend to greater radii in the circumstellar envelopes than SiO maser emission and to similar or greater radii than water masers at 22, 321 and 325 GHz. We speculate that a prominent blue-shifted feature in the WHya 183 GHz spectrum is amplifying the stellar continuum, and is located at a similar distance from the star as mainline OH maser emission. We note that the coupling of an SiO maser model to a hydrodynamical pulsating model of an AGB star yields qualitatively similar simulated results to the observations. From a comparison of the individual polarizations, we find that the SiO maser linear polarization fraction of several features exceeds the maximum fraction allowed under standard maser assumptions and requires strong anisotropic pumping of the maser transition and strongly saturated maser emission. The low polarization fraction of the H2O maser however, fits with the expectation for a non-saturated maser. Conclusions. 183 GHz H2O masers can provide strong probes of the mass loss process of evolved stars. Higher angular resolution observations of this line using ALMA Band 5 will enable detailed investigation of the emission location in circumstellar envelopes and can also provide information on magnetic field strength and structure.
|
|
| 7. |
- van Langevelde, H. J., et al.
(författare)
-
The Synergy between VLBI and Gaia astrometry
- 2018
-
Ingår i: Proceedings of Science. - 1824-8039. ; 344
-
Konferensbidrag (refereegranskat)abstract
- With the publication of Gaia DR2, 1.3 billion stars now have public parallax and proper motion measurements. In this contribution, we compare the results for sources that have both optical and radio measurements, focusing on circumstellar masers. For these large, variable and bright AGB stars, the VLBI astrometry results can be more robust. Moreover, there are a number of applications where VLBI astrometry provides unique data for studying stellar populations and Galactic structure. The BeSSel project not only provides parallax and proper motions at much larger distances than Gaia can reach, but it also uniquely samples the spiral arms of the Galaxy. The evolved stars in the BAaDE sample can potentially constrain the dynamics and stellar content of the inner bulge and bar of the Milky Way, not reachable in the optical.
|
|
