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  • 1
    In: Proceedings of the International Astronomical Union, Cambridge University Press (CUP), Vol. 13, No. S336 ( 2017-09), p. 162-167
    Abstract: In this proceeding paper, we introduce the recent results of Galactic maser astrometry by mainly focusing on those obtained with Japanese VLBI array VERA. So far we have obtained parallaxes for 86 sources including preliminary results, and combination with the data obtained with VLBA/BeSSeL provides astrometric results for 159 sources. With these most updated results we conduct preliminary determinations of Galactic fundamental parameters, obtaining R 0 = 8.16 ± 0.26 kpc and Θ 0 = 237 ± 8 km/s. We also derive the rotation curve of the Milky Way Galaxy and confirm the previous results that the rotation curve is fairly flat between 5 kpc and 16 kpc, while a remarkable deviation is seen toward the Galactic center region. In addition to the results on the Galactic structure, we also present brief overviews on other science topics related to masers conducted with VERA, and also discuss the future prospect of the project.
    Type of Medium: Online Resource
    ISSN: 1743-9213 , 1743-9221
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2017
    detail.hit.zdb_id: 2170724-8
    detail.hit.zdb_id: 232923-2
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 2
    In: Publications of the Astronomical Society of Japan, Oxford University Press (OUP), Vol. 68, No. 5 ( 2016-10-01)
    Abstract: The Hitachi and Takahagi 32 m radio telescopes (former satellite communication antennas) were so upgraded as to work at 6, 8, and 22 GHz. We developed the receiver systems, IF systems, back-end systems (including samplers and recorders), and reference systems. We measured the performance of the antennas. The system temperature including the atmosphere toward the zenith, $T_{\rm sys}^{\ast }$, is measured to be ∼30–40 K for 6 GHz and ∼25–35 K for 8 GHz. $T_{\rm sys}^{\ast }$ for 22 GHz is measured to be ∼40–100 K in winter and ∼150–500 K in summer seasons, respectively. The aperture efficiency is 55%–75% for Hitachi at 6 GHz and 8 GHz, and 55%–65% for Takahagi at 8 GHz. The beam sizes at 6 GHz and 8 GHz are ∼4${^{\circ}_{.}}$6 and ∼3${^{\circ}_{.}}$8, respectively. The side-lobe level is less than 3%–4% at 6 and 8 GHz. Pointing accuracy was measured to be better than ∼0${^{\circ}_{.}}$3 for Hitachi and ∼0${^{\circ}_{.}}$6 for Takahagi. We succeeded in VLBI observations in 2010 August, indicating good performance of the antenna. We started single-dish monitoring observations of 6.7 GHz methanol maser sources in 2012 December, and found several new sources showing short-term periodic variation of the flux density.
    Type of Medium: Online Resource
    ISSN: 2053-051X , 0004-6264
    RVK:
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2016
    detail.hit.zdb_id: 2083084-1
    detail.hit.zdb_id: 282483-8
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 3
    In: The Astrophysical Journal, American Astronomical Society, Vol. 822, No. 1 ( 2016-05-01), p. 3-
    Abstract: We present the first images of the v  = 1 and v  = 2 J  = 1 → 0 SiO maser lines taken with KaVA, i.e., the combined array of the Korean Very Long Baseline Interferometry (VLBI) Network and the VLBI Exploration of Radio Astrometry (VERA), toward the OH/IR star WX Psc. The combination of long and short antenna baselines enabled us to detect a large number of maser spots, which exhibit a typical ring-like structure in both the v  = 1 and v  = 2 J  = 1 → 0 SiO masers as those that have been found in previous VLBI observational results of WX Psc. The relative alignment of the v  = 1 and v  = 2 SiO maser spots are precisely derived from astrometric analysis, due to the absolute coordinates of the reference maser spot that were well determined in an independent astrometric observation with VERA. The superposition of the v  = 1 and v  = 2 maser spot maps shows a good spatial correlation between the v  = 1 and v  = 2 SiO maser features. Nevertheless, it is also shown that the v  = 2 SiO maser spot is distributed in an inner region compared to the v  = 1 SiO maser by about 0.5 mas on average. These results provide good support for the recent theoretical studies of the SiO maser pumping, in which both the collisional and the radiative pumping predict the strong spatial correlation and the small spatial discrepancy between the v  = 1 and v  = 2 SiO maser.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2016
    detail.hit.zdb_id: 2960-9
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2016
    In:  Publications of the Astronomical Society of Japan Vol. 68, No. 5 ( 2016-10-01)
    In: Publications of the Astronomical Society of Japan, Oxford University Press (OUP), Vol. 68, No. 5 ( 2016-10-01)
    Abstract: We have measured an annual parallax of the Mira variable R Ursae Majoris (R UMa) with the VLBI Exploration for Radio Astronomy (VERA). From the monitoring VLBI observations over a span of about two years, we detected H2O maser spots in the LSR velocity range from 37 to 42 km s−1. We derived an annual parallax of 1.97 ± 0.05 mas, and this gives a corresponding distance of 508 ± 13 pc. The VLBI maps revealed 72 maser spots distributed in an ∼110 au area around the expected stellar position. Circumstellar kinematics of the maser spots were also revealed by subtracting a systemic motion in the Hipparcos catalog from proper motions of each maser spot derived from our VLBI observations. Infrared photometry was also conducted to measure a K-band apparent magnitude, and we obtained a mean magnitude of mK = 1.19 ± 0.02 mag. Using the trigonometric distance, mK is converted to a K-band absolute magnitude of MK = −7.34 ± 0.06 mag. This result gives a much more accurate absolute magnitude for R UMa than previously provided. We solved a zero-point of the MK–log P relation for the Galactic Mira variables and obtained a relation of MK = −3.52 log P + (1.09  ±  0.14). Other long-period variables, including red supergiants, whose distances were determined with astrometric VLBI, were also compiled to explore the different sequences of the MK–log P relation.
    Type of Medium: Online Resource
    ISSN: 2053-051X , 0004-6264
    RVK:
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2016
    detail.hit.zdb_id: 2083084-1
    detail.hit.zdb_id: 282483-8
    SSG: 16,12
    Location Call Number Limitation Availability
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