• Yong Huang

      Articles written in Journal of Astrophysics and Astronomy

    • A Visual Method of Time Scale Determination using a PC for Radio Sources

      Yong Huang Jun-Hui Fan Jing Pan

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      Variability is one of the extremely observational properties. In the radio bands, variability is caused by the shock in the jet. In this case, emissions increase rapidly following an exponential curve, and then decrease rapidly also in an exponential curve. The variability time scale is important with regard to the physics carrying on in the jet. However, it is not easy to fit the light curve. In this paper, we proposed a method of light curve fitting on a PC machine, in which the theoretical exponential light curve is adopted to the observations using the least regression method. Using this method, anybody can fit the light curve and get the time scale by moving and clicking themouse.We also used this method to some light curves obtained from the archive and compared our results with those in the literature.

    • OH megamasers: dense gas & the infrared radiation field


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      To investigate possible factors related to OH megamaser formation (OH MM, $L_{{\rm H}_2{\rm O}} > 10L_{\odot}$), we compiled a large HCN sample from all well-sampled HCN measurements so far in local galaxies and identifiedwith the OH MM, OH kilomasers ($L_{{\rm H}_2{\rm O}} > 10L_{\odot}$, OH kMs), OH absorbers and OH non-detections (non-OH MM). Through comparative analysis on their infrared emission, CO and HCN luminosities (good tracers for the low-density gas and the dense gas, respectively), we found that OH MM galaxies tend to have stronger HCN emission and no obvious difference on CO luminosity exists between OH MM and non-OH MM. This implies that OH MM formation should be related to the dense molecular gas, instead of the low-density molecular gas. It can be also supported by other facts: (1) OH MMs are confirmed to have higher mean molecular gas density and higher dense gas fraction ($L_{\rm HCN}/L_{\rm CO}$) than non-OH MMs. (2) After taking the distance effect into account, the apparent maser luminosity is still correlated with the HCN luminosity, while no significant correlation can be found at all between the maser luminosity and the CO luminosity. (3) The OH kMs tend to have lower values than those of OH MMs, including the dense gas luminosity and the dense gas fraction. (4) From analysis of known data of another dense gas tracer HCO$^+$, similar results can also be obtained. However, from our analysis,the infrared radiation field can not be ruled out for the OH MM trigger, which was proposed by previous works on one small sample (Darling in ApJ 669:L9, 2007). On the contrary, the infrared radiation field should play one more important role. The dense gas (good tracers of the star formation) and its surrounding dust are heated by the ultra-violet (UV) radiation generated by the star formation and the heating of the high-density gas raises the emission of the molecules. The infrared radiation field produced by the re-radiation of the heated dust inturn serves for the pumping of the OH MM.

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      Posted on January 27, 2016

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