Abstract
Abstract Based on the accurate color excess E G BP , G RP of more than 4 million stars and the E NUV , G BP of more than 1 million stars from Sun et al., the distance and extinction of the molecular clouds (MCs) in the Magnani–Blitz–Mundy catalog at ∣b∣ > 20° are studied in combination with the distance measurement of Gaia/EDR3. The distance, as well as the color excess, is determined for 66 MCs. The color excess ratio E N U V , G B P / E G B P , G R P is derived for 39 of them, which is obviously larger and implies more small particles at smaller extinction. In addition, the scale height of the dust disk is found to be about 100 pc and becomes large at the anticenter direction due to the disk flaring.
Highlights
The study of molecular clouds, the site of star formation (Blitz & Williams 1999), is important for the information of the initial mass function of stars and the build-up of galaxies
Based on the accurate color excess EGBP,GRP of more than 4 million stars and ENUV,GBP of more than 1 million stars from Sun et al (2021), the distance and the extinction of the molecular clouds in the MBM catalog at |b| > 20◦ are studied in combination with the distance measurement of Gaia/EDR3
In 1923, Wolf (1923) first effectively describes the Wolf diagrams based on star counts in obscured vs. reference fields to determine the distance to molecular clouds, and Magnani & de Vries (1986) applied the Wolf diagrams to a small subset of MBM clouds
Summary
The study of molecular clouds, the site of star formation (Blitz & Williams 1999), is important for the information of the initial mass function of stars and the build-up of galaxies. Brand et al 1994; May et al 1997; Nakagawa et al 2005; Roman-Duval et al 2009; Garcıa et al 2014; Miville-Deschenes et al 2017) The well-known problems are the large uncertainty induced by the presence of peculiar and non-circular motions, and the ambiguity that one velocity can correspond to two distances at either side of the tangent point Another frequently used method is to find the distance to the objects associated with a cloud and to place the cloud at the same distance, for instance, many clouds have produced young OB associations of stars for which distances can be estimated. With the multi-band photometry by PanSTARRS-1 (Kaiser et al 2010) and the resultant color indexes of numerous stars, Schlafly et al (2014) derived the distances to 18 well-known star-forming regions, and 108 molecular clouds at high Galactic latitude selected from Magnani et al (1985) and Dame et al (2001) according to the breakpoint of the extinction
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