The Bok Globule BHR 160: structure and star formation

BHR 160 is a virtually unstudied cometary globule within the Sco OB4 association in Scorpius at a distance of 1600pc. It is part of a system of cometary clouds which face the luminous O star HD155806. BHR 160 is special because it has an intense bright rim. We attempt to derive physical parameters for BHR 160 and to understand its structure and the origin of its peculiar bright rim. BHR 160 was mapped in the $^{12}$CO, $^{13}$CO and C$^{18}$O (2-1) and (1-0) and CS (3-2) and (2-1) lines. These data, augmented with stellar photometry derived from the ESO VVV survey, were used to derive the mass and distribution of molecular material in BHR 160 and its surroundings. Archival mid-infrared data from the WISE satellite was used to find IR excess stars in the globule and its neighbourhood. An elongated 1' by 0.6' core lies adjacent to the globule bright rim. $^{12}$CO emission covers the whole globule, but the $^{13}$CO, C$^{18}$O and CS emission is more concentrated to the core. The $^{12}$CO line profiles indicate the presence of outflowing material near the core, but the spatial resolution of the mm data is not sufficient for a detailed spatial analysis. The BHR 160 mass estimated from the C$^{18}$O mapping is 100$\pm$50Msun(d/1.6kpc)$^2$ where d is the distance to the globule. Approximately 70 percent of the mass lies in the dense core. The total mass of molecular gas in the direction of BHR 160 is 210$\pm$(d/1.6kpc)$^2$ Msun when estimated from the more extended VVV NIR photometry. We argue that the bright rim of BHR 160 is produced by a close-by early B-type star, HD 319648, that was likely recently born in the globule. This star is likely to have triggered the formation of a source, IRS 1, that is embedded within the core of the globule and detected only in Ks and by WISE and IRAS.Comment: 19 pages, 24 figures, Accepted for publication in Astronomy and Astrophysic

Mass and motion of globulettes in the Rosette Nebula

We have investigated tiny molecular clumps in the Rosette Nebula. Radio observations were made of molecular line emission from 16 globulettes identified in a previous optical survey. In addtion, we collected images in the NIR broad-band JHKs and narrow-band Paschen beta and H2. Ten objects, for which we collected information from several transitions in 12CO and 13CO were modelled using a spherically symmetric model. The best fit to observed line ratios and intensities was obtained by assuming a model composed of a cool and dense centre and warm and dense surface layer. The average masses derived range from about 50 to 500 Jupiter masses, which is similar to earlier estimates based on extinction measures. The globulettes selected are dense, with very thin layers of fluorescent H2 emission. The NIR data shows that several globulettes are very opaque and contain dense cores. Because of the high density encountered already at the surface, the rims become thin, as evidenced by our P beta images. We conclude that the entire complex of shells, elephant trunks, and globulettes in the northern part of the nebula is expanding with nearly the same velocity of ~22 km/s, and with a very small spread in velocity among the globulettes. Some globulettes are in the process of detaching from elephant trunks and shells, while other more isolated objects must have detached long ago and are lagging behind in the general expansion of the molecular shell. The suggestion that some globulettes might collapse to form planetary-mass objects or brown dwarfs is strengthened by our finding of dense cores in several objects.Comment: 15 pages, 15 figures Astronomy and Astrophysics 201

OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters arising from a Five Day Xallarap Effect in a Candidate Planetary Microlensing Event

We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves $\chi^2$ values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters like mass-ratio, $q$, and separation, $s$, cannot be constrained well. However, we also find that the parameters for the source system like the orbital period and semi major axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of $P\sim5$ days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters.Comment: 19 pages, 7 figures, 6 tables. Accepted by A

OGLE-2019-BLG-0825:constraints on the source system and effect on binary-lens parameters arising from a five day xallarap effect in a candidate planetary microlensing event

We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ2 values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters like mass-ratio, q, and separation, s, cannot be constrained well. However, we also find that the parameters for the source system like the orbital period and semi major axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of P ∼ 5 days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters

OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters Arising from a Five-day Xallarap Effect in a Candidate Planetary Microlensing Event

We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ ^2 values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters such as mass ratio, q , and separation, s , cannot be constrained well. However, we also find that the parameters for the source system such as the orbital period and semimajor axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of P ∼ 5 days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters