This is the way
https://orcid.org/0000-0001-5574-0549* I am a Ph.D. candidate in Astronomy & Astrophysics at the Max-Planck-Institut für Radioastronomie as well as a member of the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne. My Ph.D. thesis targets on the influence of stellar objects onto the interstellar medium (ISM), with two different tools, isotope ratios and ammonia masers. Thesis advisor/supervisor: Dr. Christian Henkel, Prof. Dr. Karl Menten
Widespread non-metastable ammonia masers in the Milky Way
* With the 100-m Effelsberg telescope, we discovered NH3 (9,6) masers in CepA and G34.26+0.15 (Yan et al. 2022a, A&A, 659, A5) and widespread non-metastable NH3 maser emission toward Sagittarius B2 (Yan et al. 2022b, A&A, 666, L15). Higher-angular-resolution observations from the the Karl G. Jansky Very Large Array (JVLA) show that all of the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCHII regions.
* There exists no systematic survey to search for ammonia masers so far. We did a search for ammonia maser emission in 119 Galactic high-mass star-forming regions (HMSFRs) known to host 22 GHz H2O maser emission with the 100-m Effelsberg telescope (Yan et al. 2024). Our survey has led to the discovery of non-metastable NH3 inversion line masers toward 14 of these sources. This doubles the number of known non-metastable ammonia masers in our Galaxy, including nine new very high-excitation (J,K) = (9,6) maser sources. Additionally, we tentatively detect a new metastable NH3 (3,3) maser in G048.49 and an NH3 (7,7) maser in G029.95. Our observations reveal that all of the newly detected NH3 maser lines exhibit either blueshifted or redshifted velocities with respect to the source systemic velocities.
* So far, a total of 33 14NH3 inversion transitions and three 15NH3 inversion lines have been identified as masers in the interstellar medium (ISM). Ammonia masers are rare in the ISM compared to other maser species; that is, those of OH, H2O, and CH3OH. NH3 masers have only been detected in 47 sources. The ammonia transitions identified as masers in the ISM and the sources that are known to host ammonia masers are summarized in our recent paper (Yan et al. 2024).
Carbon and sulfur isotope ratios in the Milky Way
* Recently, we measured carbon and sulfur isotope ratios in the Milky Way with the IRAM 30-m telescope (Yan et al. 2023, A&A, 670, A98). We found that 12C/13C ratios in the central molecular zone are higher than expected from a linear fit to the disk values. While 32S/34S ratios near the Galactic center and in the inner disk are similar, this is not the case for 12C/13C, when comparing central values with those near galactocentric radii of 5 kpc. As was already known, there is no 34S/33S gradient but the average ratio of 4.35+-0.44 derived from the J = 2-1 transition lines of C34S and C33S is well below previously reported values. A comparison between solar and local interstellar 32S/34S and 34S/33S ratios suggests that the Solar System may have been formed from gas with a particularly high 34S abundance. For the first time, we report positive gradients of 32S/33S, 34S/36S, 33S/36S, and 32S/36S in our Galaxy. The predicted 12C/13C ratios from the latest Galactic chemical-evolution models are in good agreement with our results. While 32S/34S and 32S/36S ratios show larger differences at larger galactocentric distances, 32S/33S ratios show an offset across the entire inner 12 kpc of the Milky Way. Taken together, these findings provide useful guidelines for further refinements of models of the chemical evolution of the Galaxy.
Observational proposals and experiences
* As PI, I have got 1734.5 hours of observation time with the 100-m Effelsberg telescope, the 30-m IRAM telescope, the Karl G. Jansky Very Large Array, the 12-m APEX telescope, the NASA/JPL Deep Space Network DSS-43 70-m telescope, the 15-m JCMT, the ARO 12-m telescope, the 10-m SMT, and the 65-m TMRT, details are shown on my Proposal page.
* In the last four years, I have done a great number of observations (more than 2000 hours) by myself and the telescopes I have used including the Arecibo, the Effelsberg, the IRAM, the TMRT, the ARO 12m, and the SMT.
The PRECIOUS photo was taken at Effelsberg in February 2018
Left to right:
Yaoting Yan, Dr. Jiangshui Zhang, Dr. Thomas Wilson, Dr. Christian Henkel, Dr. Yan Gong
Observations with the TMRT in October 2016
With the Shanghai Tianma 65-m Radio Telescope (TMRT), we performed a large survey related to carbon isotope ratios, including sources from the Galactic Center Region to the star forming outskirts of the Milky Way well beyond the Perseus Arm. The study is based on measurements of the C-band 110-111 (4.8 GHz) and Ku-band 211-212 (14.5 GHz) K-doublet lines of H2CO and the 110-111 (4.6 GHz) line of H213CO toward a large sample of 112 Galactic molecular clouds. We obtain a linear fit of 12C/13C = 5.08(1.10)DGC + 11.86(6.60), with a correlation coefficient of 0.58. DGC refers to Galactocentric distances.
Observations with the Effelsberg in February 2018
Using the Effelsberg-100 m telescope, Zhang et al. (2017) performed a successful pilot survey on H2O maser emissiontoward a small sample of radio-bright Seyfert 2 galaxies with a redshift larger than 0.04 between January 28 and February 1 2016. The survey led to one new megamaser source and one additional possible detection, which reflects our success in selecting H2O megamaser candidates compared to previous observations. In February 2018, we confirmed the possible detection which was orignally found in 2016 (Zhang et al. 2017) as a new H2O megamaser, and 10 tentative masers were detected (Zhang et al. in preparation).