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Sh 2-54, NGC 6604, Serpens Cauda

Sh 2-54, NGC 6604, Serpens Cauda

530 mm f/5 14 hours, June 2013, Photograph

NGC 6604 and Serpens OB2 — NGC 6604 is a young star cluster in the constellation Serpens Cauda with an age of 4-5 Myr and a distance of about 1.7 kpc. At this distance, NGC 6604 is located at a galactocentric distance of 6.9 kpc, which places it on the outer boundary of the Carina-Sagittarius spiral arm, about 65 pc above the Galactic plane. NGC 6604 forms the densest part of the wider Serpens OB2 association, which contains about 100 hot O and B-type stars. From Reipurth, "The Young Cluster NGC 6604 and the Serpens OB2 Association", Handbook of Star Forming Regions, Volume II: The Southern Sky, Astronomical Society of the Pacific Monograph Publications, Monograph 5, Edited by Bo Reipurth, p. 590-598, 2008.

The central star of NGC 6604 is MY Ser, an O8Ib(f)p system. It is a eclipsing pair of two O5-8V main-sequence stars with a 3 day period together with a more distant very luminous O8I supergiant star. X-ray data show a significant X-ray luminosity excess most likely due to colliding winds. HD 168112 is another prominent member of the NGC 6604 cluster. It is an O5.5III(f) giant star with nonthermal radio emission and strong X-ray emission, which is best understood if the star is a binary with wind-wind collisions, however, there is no evidence for binarity. From Reipurth, "The Young Cluster NGC 6604 and the Serpens OB2 Association", Handbook of Star Forming Regions, Volume II: The Southern Sky, Astronomical Society of the Pacific Monograph Publications, Monograph 5, Edited by Bo Reipurth, p. 590-598, 2008.

Sh 2-54 — The massive stars of the Serpens OB2 assocation ionize the major HII region Sh 2-54. The ionized and neutral gas found in the region have the same velocity, and there may be larger connections between Sh 2-54 and the neighboring M16 and M17 HII regions outside the photograph. From Reipurth, "The Young Cluster NGC 6604 and the Serpens OB2 Association", Handbook of Star Forming Regions, Volume II: The Southern Sky, Astronomical Society of the Pacific Monograph Publications, Monograph 5, Edited by Bo Reipurth, p. 590-598, 2008.

Serpens OB2 Thermal Chimney — A major thermal chimney extends from NGC 6604 and the Serpens OB2 association out of the Galactic plane. It has dimensions of roughly 20 pc by 200 pc, has a mean electron temperature of about 4000 K, and a continuous decrease of mean electron density from about 15 cm⁻³ near Sh 2-54 to 1-2 cm⁻³ in the most distant parts. The known OB stars in the association are capable of providing the kinetic energy and the number of ionizing photons required to form the chimney. From Forbes, "The Serpens OB2 Association and its Thermal "Chimney", The Astronomical Journal, 120:2594-2608, 2000 November.

Min 1-88 — The small nebula Min 1-88 is the brightest part of the Sh 2-54 HII region and is located within a cometary globule in the molecular cloud that rims the NGC 6604 cluster. A group of infrared sources and a young loose cluster are centered on Min 1-88. It appears that Min 1-88 is a case of second-generation star formation triggered by the NGC 6604 cluster and perhaps also the Serpens OB2 association. From Reipurth, "The Young Cluster NGC 6604 and the Serpens OB2 Association", Handbook of Star Forming Regions, Volume II: The Southern Sky, Astronomical Society of the Pacific Monograph Publications, Monograph 5, Edited by Bo Reipurth, p. 590-598, 2008.

CV Ser — The Wolf-Rayet binary CV Serpentis (WR113, WC8d + O8-9IV) has been a source of mystery since it was shown that its atmospheric eclipses change with time over decades, in addition to its sporadic dust production. Observations with the MOST space telescope in 2009 show two consecutive eclipses over the 29 day orbit, with varying depths. Assuming these depth variations are entirely due to electron scattering in the beta velocity law wind, an unprecedented 62% increase in mass-loss rate is observed over one orbital period. Alternatively, no change in mass-loss rate would be required if a small fraction of the carbon ions in the wind globally recombined and coagulated to form carbon dust grains. However, it remains a mystery as to how this could occur. There also seems to be evidence for the presense of corotating interaction regions in the WR wind, implying a potential rotation period of the WR star of 1.6 day. From David-Uraz et al., "Using MOST to reveal the secrets of the mischevious Wolf-Rayet binary CV Ser", Monthly Notices of the Royal Astronomical Society, 426(3):1720-1730, 2012 November.

Coordinates: RA 18h 19.1m, Dec -11° 59’, PA +0° 28’
Field of view: 1° 56’ x 1° 28’
Image scale: 4.2” / pixel

Date: June 2013
Location: Delamar Mountains, Nevada
Exposure: 21 x 40 minutes (14 hours), binned 2 x 2 at -20° C

Zenith SQM: 21.6 mag / "²
Guiding error: 0.9" rms
Star FWHM: 4.8", histogram
Star eccentricity: 0.39
Camera noise: 15 e- rms
Background noise: 25 e- rms
Subframe location: 502 e-
Subframe scale: 230 e-

Telescope: Takahashi FSQ-106EDX 530 mm f/5
Camera: Quantum Scientific Imaging 683wsg
Filter: Astrodon H-alpha, 3 nm bandwidth
Focuser: Finger Lakes Instrumentation Atlas, Spike-a Bahtinov Mask
Guider: Santa Barbara Instrument Group ST-i
Flats: Alnitak Astrosystems Flat-Man
USB: Icron Ranger 2122, Moxa UPort 404
Mount: Takahashi EM-400 Temma2M
Acquisition: Diffraction Limited MaxIm DL, CCDAstro Temma, ASCOM Platform
Processing: Pleiades Astrophoto PixInsight, MathWorks MATLAB, IHRP Platform