Archive for dark nebulae

Onset of ice formation in the Pipe nebula

Posted in astronomy with tags , , , on December 15, 2017 by Tim Kendall

In a recent paper, Goto et al., (preprint) have used infrared absorption spectroscopy of background stars to probe ice formation on grains in the Pipe nebula (APOD image and credits), detecting water ice absorption in seven out of 21 lines of sight investigated. The peak optical depths of the water ice are about half as large as those on the sources in Taurus with similar visual extinctions. One possible explanation (among others) is that the formation of the ice mantle has just started, that is, the Pipe Nebula is in an earlier phase of ice evolution than Taurus is. Alternatively the interstellar radiation field impinging on the Pipe nebula is larger than that on the Taurus molecular cloud, or the visual extinction through the Pipe nebula may have been overestimated. From the abstract:

Spectroscopic studies of ices in nearby star-forming regions indicate that ice mantles form on dust grains in two distinct steps, starting with polar ice formation (water rich) and switching to apolar ice (CO rich). We test how well the picture applies to more diffuse and quiescent clouds where the formation of the first layers of ice mantles can be witnessed. Medium-resolution near-infrared spectra are obtained toward background field stars behind the Pipe Nebula. The water ice absorption is positively detected at 3.0 micron in seven lines of sight out of 21 sources for which observed spectra are successfully reduced. The peak optical depth of the water ice is significantly lower than those in Taurus with the same visual extinction. The source with the highest water-ice optical depth shows CO ice absorption at 4.7 micron as well. The fractional abundance of CO ice with respect to water ice is 16+7-6 %, and about half as much as the values typically seen in low-mass star-forming regions. A small fractional abundance of CO ice is consistent with some of the existing simulations. Observations of CO2 ice in the early diffuse phase of a cloud play a decisive role in understanding the switching mechanism between polar and apolar ice formation.

Advertisements

Young stars and dusty nebulae in Taurus

Posted in astronomy with tags , , on April 22, 2017 by Tim Kendall

Image and text credit: APOD: Lloyd L. Smith, Deep Sky West. This complex of dusty nebulae lingers along the edge of the Taurus molecular cloud, a mere 450 light-years distant. Stars are forming on the cosmic scene. Composed from almost 40 hours of image data, the 2 degree wide telescopic field of view includes some youthful T-Tauri class stars embedded in the remnants of their natal clouds at the top. Millions of years old and still going through stellar adolescence, the stars are variable in brightness and in the late phases of their gravitational collapse. Their core temperatures will rise to sustain nuclear fusion as they grow into stable, low mass, main sequence stars, a stage of stellar evolution achieved by our middle-aged Sun about 4.5 billion years ago. Another youthful variable star, V1023 Tauri, can be spotted in the lower part of the image. Within its yellowish dust cloud, it lies next to the striking blue reflection nebula Cederblad 30, also known as LBN 782. Above the bright bluish reflection nebula is dusty dark nebula Barnard 7.

Dark nebulae: multiwavelength imaging of Barnard 68

Posted in astronomy with tags , on December 14, 2014 by Tim Kendall

B72_RGB_m
Image credit: Emil Ivanov. The field shows the Snake Nebula, Barnard 72, together with B68, B69, B70 and B74. These nebulae were catalogued first by the American E.E. Barnard in the early years of the last century.

eso9934bImage credit: ESO/SOFI

Barnard 68 is a dark cloud situated at a distance of about 500 light-years (160 pc) towards the southern constellation Ophiuchus (The Serpent-holder). This image represents the sky area of the so-called Bok globule Barnard 68 – nicknamed the Dark Cloud – imaged in six different wavebands, clockwise from the blue to the near-infrared spectral region. Three of these frames (“blue” B-band at wavelength 440 nm = 0.44 µm; “green-yellow” V-band at 0.55 µm; near-infrared I-band at 0.90 µm) were obtained with the FORS1 instrument at the VLT ANTU telescope and three with SOFI at the NTT through near-infrared filters (J-band at 1.25 µm; H-band at 1.65 µm; Ks-band at 2.16 µm). It is evident that the obscuration caused by the cloud diminishes dramatically with increasing wavelength. Since the outer regions of the cloud are less dense than the inner ones, the apparent size of the cloud also decreases, as more background stars shine through the outer parts. Each frame covers an area of 4.9 x 4.9 arcmin². North is up and East is left.

Dark “doodad” nebula and globular cluster NGC 4372

Posted in astronomy with tags on December 24, 2013 by Tim Kendall

doodad_ederL
Located in the southern constellation of Musca, the Fly, this dark nebula spans nearly three degrees on the sky and is one of the finest examples of its kind. The original image credit (© Ivan Eder 2012) is here and the nebula has its own Wikipedia entry here.