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| LDN 673 | |
|---|---|
| Name | LDN 673 |
| Type | Dark nebula |
| Epoch | J2000 |
| Constellation | Aquila |
| Distance | ~300–700 pc |
| Discoverer | Lynds |
| Designation | Lynds Dark Nebula 673 |
LDN 673 is a dark molecular cloud cataloged in the Lynds Dark Nebula compilation. It is a compact, filamentary cloud complex that has been the subject of studies in molecular chemistry, star formation, and submillimeter mapping. The cloud lies projected against the Milky Way in Aquila and has been observed across radio, infrared, and optical wavelengths by a range of facilities.
LDN 673 appears as a high-opacity extinction feature in photographic surveys and as dense molecular emission in millimeter-wave maps. Surveys that include the cloud connect it to broader studies of molecular clouds such as those by the Two Micron All-Sky Survey (2MASS), the Spitzer Space Telescope, and the James Clerk Maxwell Telescope. Researchers contrast LDN 673 with better-known clouds like the Taurus Molecular Cloud and the Orion Molecular Cloud Complex to probe differences in chemistry, core mass function, and low-mass star formation efficiency. The region has been used to test models developed by groups at institutions such as the Harvard–Smithsonian Center for Astrophysics, the Max Planck Institute for Astronomy, and the National Radio Astronomy Observatory.
LDN 673 is projected in the constellation Aquila and is often associated spatially with nearby dark clouds cataloged by Bok and later compilations such as the Barnard Catalogue. It shows high visual extinction (AV) values typical of dense cores identified in studies at the Institut de Radioastronomie Millimétrique (IRAM) and the Onsala Space Observatory. Morphologically, the complex exhibits multiple clumps and filaments with sizes from 0.1 pc to several parsecs, comparable to structures seen in the Pipe Nebula and the California Nebula within their densest subregions. Mass estimates derived from CO isotopologue mapping and dust continuum emission place individual cores in the range of subsolar to a few tens of solar masses, similar to cores cataloged by the Bolocam Galactic Plane Survey and the Herschel Space Observatory programs.
LDN 673 contains a mix of starless and protostellar cores; embedded young stellar objects identified with infrared facilities include Class 0 and Class I candidates analogous to sources cataloged in the c2d Spitzer Legacy Survey. Chemical surveys reveal rich molecular inventories: detections include tracers such as CO, 13CO, C18O, NH3, N2H+, CCS, and complex organic molecules also reported in surveys by teams at the Nobeyama Radio Observatory and the Princeton University Observatory. Comparisons are often drawn with chemical ages inferred for cores in Perseus and Ophiuchus by groups led from the Max Planck Institute for Radio Astronomy and the University of Arizona. The balance of molecules sensitive to depletion and desorption processes indicates regions of both active freeze-out onto dust grains and zones of reactive gas-phase chemistry, making the cloud a laboratory for astrochemical models developed at institutions like the California Institute of Technology.
LDN 673 has been observed in continuum and spectral lines with instruments including the James Clerk Maxwell Telescope (SCUBA), the IRAM 30m telescope, the Very Large Array, and the Submillimeter Array. Infrared point-source catalogs from WISE and Spitzer supplied photometry used by researchers from the University of Chicago and the University of Colorado Boulder to classify embedded sources. Large-scale surveys such as the CO Galactic Plane Survey and targeted programs by the Kitt Peak National Observatory provided CO isotopologue maps that reveal velocity-coherent structures and filamentary networks. Polarimetric measurements from instruments associated with the University of Hertfordshire and the Institute for Astronomy, University of Hawaii have been used to probe magnetic field morphology in dense filaments, linking to theoretical work from groups at the University of Cambridge and the University of Bonn.
Distance estimates to the cloud complex span a range due to line-of-sight confusion with other Aquila Rift structures. Parallax measurements of embedded young stars from the Very Long Baseline Array and extinction-distance methods using Gaia stellar catalogs have helped narrow the distance to roughly a few hundred parsecs, often quoted in the literature as between ~300 and ~700 pc, comparable to distance estimates for other parts of the Aquila Rift. Kinematic studies using CO, NH3, and N2H+ lines reveal linewidths and centroid velocities consistent with subsonic to transonic internal motions like those measured in the Pipe Nebula and the Lupus Cloud Complex. Analyses by teams at the Max Planck Institute for Astronomy and the National Astronomical Observatory of Japan interpret these kinematics in the context of turbulence-regulated star formation scenarios developed by researchers at the Princeton University and the University of California, Berkeley.
LDN 673 sits within the broader Aquila Rift environment and is spatially related to nearby nebulae and dark clouds cataloged by astronomers affiliated with the Lowell Observatory and the Australian National University. Embedded sources and outflow activity link the cloud to stellar feedback phenomena studied in regions like the Orion Nebula and the Rho Ophiuchi cloud complex. Several protostellar outflows detected in CO and SiO lines have been compared to outflows characterized by researchers at the Max Planck Institute for Astronomy and the Harvard–Smithsonian Center for Astrophysics. The cloud’s placement in the Galactic plane places it within the observational purview of surveys by the European Space Agency and national facilities such as the National Science Foundation-funded observatories.