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تسجيل مستخدم جديدThe Extinction and Distance of the MBM Molecular Clouds at High Galactic Latitude
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Based on the accurate color excess $E_{rm G_{BP},G_{RP}}$ of more than 4 million stars and $E_{rm NUV,G_{BP}}$ of more than 1 million stars from citet{2021ApJS..254...38S}, the distance and the extinction of the molecular clouds in the MBM catalog at $|b|>20^{circ}$ are studied in combination with the distance measurement of emph{Gaia}/EDR3. The distance as well as the color excess is determined for 66 molecular clouds. The color excess ratio $E_{rm G_{BP},G_{RP}}/E_{rm NUV,G_{BP}}$ 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.
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Extinction in ultraviolet is much more significant than in optical or infrared, which can be very informative to precisely measure the extinction and understand the dust properties in the low extinction areas. The high Galactic latitude sky is such a
n area, important for studying the extragalactic sky and the universe. Based on the stellar parameters measured by the LAMOST and GALAH spectroscopy and the ultraviolet photomery by the emph{GALEX} space telescope, the extinction of 1,244,504 stars in the emph{GALEX}/NUV band and 56,123 stars in the emph{GALEX}/FUV band are calculated precisely. textbf{The error of color excess is 0.009, 0.128 and 0.454 mag for $E_{rm G_{BP}, G_{RP}}$, $E_{rm NUV,G_{BP}}$ and $E_{rm FUV,G_{BP}}$ respectively.} They delineates the emph{GALEX}/NUV extinction map of about a third of the sky mainly at the high Galactic latitude area with an angular resolution of $sim 0.4,, rm deg$. The mean color excess ratio in the entire sky areas is derived to be 3.25, 2.95 and -0.37 for $E_{{rm NUV,G_{BP}}} / E_{{rm G_{BP},G_{RP}}}$, $E_{{rm FUV,G_{BP}}} / E_{{rm G_{BP},G_{RP}}}$ and $E_{{rm FUV,NUV}} / E_{{rm G_{BP},G_{RP}}}$ respectively, which is in general agreement with the previous works, and their changes with the Galactic latitude and the interstellar extinction are discussed.
In this chapter we review the young stars and molecular clouds found at high Galactic latitudes $(|b| ge 30^circ)$. These are mostly associated with two large-scale structures on the sky, the Gould Belt and the Taurus star formation region, and a han
dful of molecular clouds including MBM 12 and MBM 20 which, as a population, consist of the nearest star formation sites to our Sun. There are also a few young stars that are found in apparent isolation far from any molecular cloud. The high latitude clouds are primarily translucent molecular clouds and diffuse Galactic cirrus with the majority of them seen at high latitude simply due to their proximity to the Sun. The rare exceptions are those, like the Draco and other intermediate or high velocity clouds, found significantly above or below the Galactic plane. We review the processes that result in star formation within these low density and extraplanar environments as well as the mechanisms for production of isolated T Tauri stars. We present and discuss the known high-latitude stellar nurseries and young stellar objects.
Careful analyses of photometric and star count data available for the nine putative young clusters identified by Camargo et al. (2015, 2016) at high Galactic latitudes reveal that none of the groups contain early-type stars, and most are not signific
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