Probing Effect of External UV Radiation on Young Stellar and Substellar Mass Objects: Is Orion a Special Place for Observing External Photoevaporation of Disks? Orion A Star Forming Regions NGC 1977 provides a milder radiation environment than Orion Nebula Cluster (ONC): ONCprovides strong radiation environment (with multiple O stars), since a B1 star is the highest mass star in NGC 1977. Compared to θ1 Ori C (O6.5V), surroundings of 42 Ori (B1V) has ~30 times lower FUV field, yet we find photoevaporation playing an important role on YSO evolution. L1641 which has similar age as NGC 1977 and ONC provide weaker UV environment. Proplyds in NGC 1977 30’ north of Orion Nebula Age: ~1-1.5 Myr (similar to ONC) Difference between Orion Nebula and NGC 1977: No O star! B1V is the earliest type star in the region FUV field ~ 3,000 G0 Proplyds are found for the first time near a B star! J. Serena Kim (Univ. of Arizona), Min Fang (Univ. of Arizona), Josh Eisner (Univ. of Arizona), Ilaria Pascucci (Univ. of Arizona), Daniel Apai (Univ. of Arizona), Cathie Clarke (IoA, Cambridge), Stefano Facchini (MPE), Carlo Manara (ESA/ESTEC), Marina Kounkel (WWU), Kevin Covey (WWU), NExSS/EOS team, and APOGEE2-YSO team Orion B 1 Myr Barnard’s loop OB 1a 6-10 Myr OB 1b 5 Myr Orion Nebula σOri 3-4 Myr NGC 2068 2071 NGC 2024 NGC1980 NGC1977 ~1-1.5Myr ~1-1.5 Myr 1-2 Myr ~1.5 Myr 25 Ori 7-10 Myr L1641 Photoevaporating Protoplanetary Disks Is Orion SFRs at special time to observe Photoevaporating YSOs? Orion Nebula has the most number of extensively studied proplyds around Trapezium stars, especially around θ1 Ori C (O6.5). There are only a few proplyds known in other star forming regions all around O stars (e.g.,Balog et al. 2006, Koenig et al. 2006, Fang et al. 2012). NGC 1977 has the 2nd most number of proplyds found so far. There are handful of proplyds in other regions but in small numbers. Disks in ONC near θ1 Ori C are truncated and smaller than other SFRs! A Candidate Planetary Mass Proplyd in ONC: Proplyd 133-353 Star forming regions and approximate ages of SFRs in Orion. Background image is courtesy of Roberto Bernal Andreo In the table… #4 and 5 has K ~ 17-18mag (from UKIRT, Kim et al. in prep). These are below Spitzer detection limit (Megeath et al. 2012) and we place an upper limit: Mproplyd< 0.015Msun Proplyds in NGC 1977 (HST/ACS image F658N) from Kim et al. (2016). The yellow arrows point toward the B1 star, 42 Ori. NGC 1977. The blue stars are the locations of B stars and the red circles are the locations of proplyds (Kim et al. 2016). The other symbols are the candidate YSOs (Fang, Kim et al. in prep.) Modeling of proplyds Model: from Facchini et al. (2016) For B1 star (~10 M⦿, NLy = 1045/s, LFUV= 2x1037 erg/ s.) (Diaz-Miller et al. 1998, Armitage 2000) FFUV ~ 3000 G0 at d = 0.2-0.3 pc from B1 star Ṁphot ~ 10-8 - 10-9 M⦿ yr-1 Rdisk ~ 40 - 50 AU RIF ~ 70 - 400 AU for Rdisk ~ 40 – 50 AU References Balog, Z., Rieke, G. H., Su, K. Y. L., et al. 2006, ApJL, 2006, 650, 83 DaRio, M.. Tan, J. C., Covey, K. R. et al. 2016, ApJ, 818, 59 Eisner, J. et al. 2018, ApJ, 860, 77 Facchini, S., Clarke, C. J., & Bisbas, T. G. 2016, MNRAS, 457, 3593 Fang, M. van Boekel, R., King, R. R. et al. 2012, A&A, 539, 119 Fang, M., Kim, J. S., Pascucci, I. et al. 2016, ApJ. 833, L16 Fang, M. Kim, J. S., Pascucci, I. et al. 2017, ApJ, 153, 188 Kounkel, M. et al. 2018, AJ, accepted Kim, J. S., Clarke, C. J., Fang, M., & Facchini, S. 2016, ApJ, 826, L15 Megeath S. T., Gutemuth, R., Muzerolle, J. et al., 2012, AJ, 144, 192 This work benefits from the EOS NExSS collaboration. We acknowledge the European Research Council under ERC-2013-ADG. The HST data presented in this paper were obtained from the Mikulski Archive for Space Telescopes ( MAST) at https:// archive.stsci.edu/hst/ . Background image credit: ESA/NASA/JPL-Caltech Proplyd 133-353 is near θ1 Ori C at the center of ONC. Our Near-IR spectroscopic data found it to be M9.5 And have a mass of ~13 Jupiter mass at an age o