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Register a new userHigh-resolution CARMA Observation of Molecular Gas in the North America and Pelican Nebulae
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We present the first results from a CARMA high-resolution $^{12}$CO(1-0), $^{13}$CO(1-0), and C$^{18}$O(1-0) molecular line survey of the North America and Pelican (NAP) Nebulae. CARMA observations have been combined with single-dish data from the Purple Mountain 13.7m telescope to add short spacings and produce high-dynamic-range images. We find that the molecular gas is predominantly shaped by the W80 HII bubble that is driven by an O star. Several bright rims are probably remnant molecular clouds heated and stripped by the massive star. Matching these rims in molecular lines and optical images, we construct a model of the three-dimensional structure of the NAP complex. Two groups of molecular clumps/filaments are on the near side of the bubble, one being pushed toward us, whereas the other is moving toward the bubble. Another group is on the far side of the bubble and moving away. The young stellar objects in the Gulf region reside in three different clusters, each hosted by a cloud from one of the three molecular clump groups. Although all gas content in the NAP is impacted by feedback from the central O star, some regions show no signs of star formation, while other areas clearly exhibit star formation activity. Other molecular gas being carved by feedback includes the cometary structures in the Pelican Head region and the boomerang features at the boundary of the Gulf region. The results show that the NAP complex is an ideal place for the study of feedback effects on star formation.
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The Bajamar Star is an early O star that ionizes the North America/Pelican Nebulae. In projection, it is near the geometric center of the H II region, but appears to lie outside any of the main stellar subgroups. Furthermore, in Gaia DR2, there were slight discrepancies between this star and the rest of the system in parallax (2$sigma$ larger) and relative tangential velocity (~6 km/s). Using Gaia EDR3, we find that the parallax discrepancy has disappeared, but the velocity difference remains. These results are consistent with the star having escaped from a subgroup.
We present a spectroscopic survey of over 3400 potential members in the North America and Pelican nebulae (NAP) using several low-resolution ($Rapprox$ 1300-2000) spectrographs: Palomar/Norris, WIYN/HYDRA, Keck/DEIMOS, and MMT/Hectospec. We identify 580 young stars as likely members of the NAP region based on criteria involving infrared excess, Li I 6708 absorption, X-ray emission, parallax, and proper motions. The spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main sequence stars, or model atmospheres. The templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. We use the spectral types with archival photometry to derive $V$-band extinction and stellar luminosity. From the H-R diagram, the median age of the young stars is about 1 Myr, with a luminosity dispersion of $sim$0.3--0.4 dex. We investigate the photometric variability of the spectroscopic member sample using ZTF data, and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. While larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. The measured ages of stellar kinematic groups, combined with inferred ages for embedded stellar populations revealed by Spitzer, suggests a sequential history of star formation in the NAP region.
We present observations of near-infrared 2.12 micro-meter molecular hydrogen outflows emerging from 1.1 mm dust continuum clumps in the North America and Pelican Nebula (NAP) complex selected from the Bolocam Galactic Plane Survey (BGPS). Hundreds of individual shocks powered by over 50 outflows from young stars are identified, indicating that the dusty molecular clumps surrounding the NGC 7000 / IC 5070 / W80 HII region are among the most active sites of on-going star formation in the Solar vicinity. A spectacular X-shaped outflow, MHO 3400, emerges from a young star system embedded in a dense clump more than a parsec from the ionization front associated with the Pelican Nebula (IC 5070). Suspected to be a binary, the source drives a pair of outflows with orientations differing by 80 degrees. Each flow exhibits S-shaped symmetry and multiple shocks indicating a pulsed and precessing jet. The `Gulf of Mexico located south of the North America Nebula (NGC 7000), contains a dense cluster of molecular hydrogen objects (MHOs), Herbig-Haro (HH) objects, and over 300 YSOs, indicating a recent burst of star formation. The largest outflow detected thus far in the North America and Pelican Nebula complex, the 1.6 parsec long MHO 3417 flow, emerges from a 500 Solar mass BGPS clump and may be powered by a forming massive star. Several prominent outflows such as MHO 3427 appear to be powered by highly embedded YSOs only visible at a wavelength > 70 micro-meters. An `activity index formed by dividing the number of shocks by the mass of the cloud containing their source stars is used to estimate the relative evolutionary states of Bolocam clumps. Outflows can be used as indicators of the evolutionary state of clumps detected in mm and sub-mm dust continuum surveys.
We present a 9 deg^2 map of the North American and Pelican Nebulae regions obtained in all four IRAC channels with the Spitzer Space Telescope. The resulting photometry is merged with that at JHKs from 2MASS and a more spatially limited $BVI$ survey from previous ground-based work. We use a mixture of color- color diagrams to select a minimally contaminated set of more than 1600 objects that we claim are young stellar objects (YSOs) associated with the star forming region. Because our selection technique uses IR excess as a requirement, our sample is strongly biased against inclusion of Class III YSOs. The distribution of IRAC spectral slopes for our YSOs indicates that most of these objects are Class II, with a peak towards steeper spectral slopes but a substantial contribution from a tail of flat spectrum and Class I type objects. By studying the small fraction of the sample that is optically visible, we infer a typical age of a few Myr for the low mass population. The young stars are clustered, with about a third of them located in eight clusters that are located within or near the LDN 935 dark cloud. Half of the YSOs are located in regions with surface densities higher than 1000 YSOs / deg^2. The Class I objects are more clustered than the Class II stars.
We observed the G305 star forming complex in the $J=3text{-}2$ lines of $^{12}$CO and $^{13}$CO to investigate how molecular gas surrounding the central stellar clusters is being impacted by feedback. The APEX telescopes LAsMA multi-beam receiver was used to observe the region. Excitation temperatures and column density maps were produced. Combining our data with data from the SEDIGISM survey resulted in a $^{13}$CO $J=3text{-}2/2text{-}1$ excitation map. To verify whether feedback from stellar clusters is responsible for exciting the gas, the distribution of CO excitation was compared with that of 8$,murm{m}$ emission imaged with Spitzer, which is dominated by UV-excited emission from PAHs. Line centroid velocities, as well as stacked line profiles were examined to investigate the effect of feedback on the gas dynamics. Line profiles along radially outward directions demonstrate that the excitation temperature and $^{13}$CO $J=3text{-}2/2text{-}1$ ratio increase steeply by factors of $sim,2-3$ at the edge of the denser gas traced by $^{13}$CO that faces the hot stars at the center of the complex and steadily decreases away from it. Column density also increases at the leading edge, but does not always decrease steadily outward. Regions with higher 8$,murm{m}$ flux have higher median excitation temperatures, column densities and $^{13}$CO $J=3text{-}2/2text{-}1$ ratio. The centroid velocity probability distribution function of the region shows exponential wings, indicative of turbulence driven by strong stellar winds. Stacked spectra in regions with stronger feedback have higher skewness and narrower peaks with pronounced wings compared to regions with weaker feedback. Feedback from the stellar cluster in G305 has demonstrable effects on the excitation as well as on the dynamics of the giant molecular cloud.
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