Chamaeleon Dark Cloud Research Articles

Near‐Infrared Extinction Law in the ρ Ophiuchi and Chamaeleon Dark Clouds

We determine and compare the color excess ratios EJ-H/E for the ρ Ophiuchi and Chamaeleon dark clouds with the J-, H-, and Ks-band simultaneous camera, SIRIUS, on the IRSF 1.4 m telescope at SAAO. Determining accurate ratios is indispensable for discussions of the extinction law. However, previous surveys suffered from uncertainties in transforming one photometric system to another when comparing data on different systems. To overcome the problem, we observe both clouds in exactly the same photometric system on the same telescope, greatly simplifying the comparison of the extinction laws between two clouds. From our surveys covering about 1.56 deg2 (ρ Oph) and 2.77 deg2 (Chamaeleon), which are complete for J ~ 19.0, H ~ 18.3, and KS ~ 17.0 mag at a 10 σ limiting magnitude, we did not find a significant difference in the extinction law EJ-H/E for the two clouds, in contrast to previous work. From calculations of a model star with the effects of filter and atmosphere transmissions, the differences of the color excess ratios EJ-H/EH-K for two clouds described in the past literature can be attributed to the different photometric systems so far employed. We also note a change of the color excess ratio that occurs with increasing optical depth.

Clumpy filaments of the Chamaeleon I cloud: C$\mathsf{^{18}}$O mapping with the SEST

The Chamaeleon  dark cloud (Cha ) has been mapped in C 18 O( J = 1−0) with an angular resolution of 1 � using the SEST telescope. The large scale structures previously observed with lower spatial resolution in the cloud turn into a network of clumpy filaments. The automatic Clumpfind routine developed by Williams et al. (1994) is used to identify individual clumps in a consistent way. Altogether 71 clumps were found and the total mass of these clumps is 230 M� . The dense de- tected with the NANTEN telescope (Mizuno et al. 1999) and the very cold cores detected in the ISOPHOT serendipity survey (Toth et al. 2000) form parts of these filaments but decompose into numerous clumps. The filaments are preferentially ori- ented at right angles to the large-scale magnetic field in the region. We discuss the cloud structure, the physical characteristics of the clumps and the distribution of young stars. The observed clump mass spectrum is compared with the predictions of the turbulent fragmentation model of Padoan & Nordlund (2002). Agreement is found if fragmentation has been driven by very large-scale hypersonic turbulence, and if by now it has had time to dissipate into modestly supersonic turbulence in the inter- clump gas. According to numerical simulations, large-scale turbulence should have resulted in filamentary structures as seen in Cha . The well-oriented magnetic field does not, however, support this picture, but suggests magnetically steered large-scale collapse. The origin of filaments and clumps in Cha  is thus controversial. A possible solution is that the characterization of the driving turbulence fails and that in fact different processes have been effective on small and large scales in this cloud.

A study of the stellar population in the Chamaeleon dark clouds

The properties of the stellar population in the Chamaeleon dark clouds are discussed. Spectral energy distributions, based on the extant photometric and spectroscopic data base and IRAS fluxes measured from coadded data taken at the position of each star, and spectral types allow placement of the stars in an H-R diagram. The age and mass distributions and the luminosity function for the Chamaeleon stars are compared to those in the Taurus-Auriga dark clouds and are found to be similar. A small subsample (eight of 36) of the Chamaeleon stars show unusual spectral energy distributions which seem best interpreted as arising from circumstellar disks whose inner regions (R(in)) is less than 30-50 stellar radii) area devoid of material. The X-ray properties of this sample of premain-sequence objects are compared to those of other premain-sequence samples, as well as to the Hyades and the Pleiades main-sequence stars.

Soft X-ray observations of pre-main-sequence stars in the Chamaeleon dark cloud

Einstein IPC observations of the nearby Chamaeleon I star forming cloud show 22 well-resolved soft X-ray sources in a 1x2 deg region. Twelve are associated with H-alpha emission line pre-main sequence (PMS) stars, and four with optically selected PMS stars. Several X-ray sources have two or more PMS stars in their error circles. Optical spectra were obtained at CTIO of possible stellar counterparts of the remaining X-ray sources. They reveal 5 probable new cloud members, K7-MO stars with weak or absent emission lines. These naked X-ray selected PMS stars are similar to those found in the Taurus-Auriga cloud. The spatial distributions and H-R diagrams of the X-ray and optically selected PMS stars in the cloud are very similar. Luminosity functions indicate the Chamaeleon stars are on average approximately 5 times more X-ray luminous than Pleiad dwarfs. A significant correlation between L sub x and optical magnitude suggests this trend may continue within the PMS phase of stellar evolution. The relation of increasing X-ray luminosity with decreasing stellar ages is thus extended to stellar ages as young as 1 million years.

The Chamaeleon Dark Clouds Complex: Preliminary Analysis of the Colour Excesses E(b-y) Towards the Selected Area 203

The Chamaeleon dark clouds form a large complex of interstellar obscuring material situated at ≈ 15° below the galactic plane. Although it is accepted as being one of the closest low-mass star formation region to the Sun, its distance has been debated issues. The proposed distance is in general dependent on the value assumed for the ratio of total-to-selective extinction, which in the Chamaeleon clouds has proved controversial, leading to distances estimates ranging from 115 to 215 pc.

Studies of the chamaeleon star-forming region III. The distance to the dark cloud and the spectral energy distribution of HD 97048 and HD 97300

Using a method which will be explained in detail by Steenman and The (1989) the extinction law towards several stars indicating the distance of the Chamaeleon dark cloud was determined. This has also been done for HD 97048 and HD 97300, which turn out to be anomalous with a ratio of total to selective extinctionR∼5.0. In studies involving the distance of the Chamaeleon dark cloud we propose to use 150±15 pc. The extinction-free spectral energy distribution of HD 97300 does not show the presence of a hot dust shell of 2750 K, which was found by Theet al. (1986) in a previous study.

Infrared companions to pre-main sequence stars

We report 1.2, 1.6, 2.2 and 3.6 μm slit scan observations of the young low-luminosity stars Elias 22 (also known as GSS 31) in the Rho Ophiuchus dark cloud and Glass I in the Chamaeleon dark cloud. We discovered an infrared companion to Elias 22 at a projected separation of 2.0 arcsec (320 AU) and an optical/infrared companion to Glass I at a projected separation of 2.9 arcsec (410 AU). The companion of Elias 22 is a very cool optically almost invisible object (~1000 K) less luminous than the primary, while the companion to Glass I is an optically visible late-type star with an infrared excess so large that it is actually bolometrically brighter than the primary. In both cases the infrared excess is likely to be due to hot circumstellar dust grains heated by a central young star (much more obscured in the case of Elias 22 than in the case of Glass I). We outline a new method to determine the mass ratio of such systems assuming that both components lie on an isochrone in the H-R diagram. If the companions are in a bound orbit, the estimated specific angular momentum exceeds or is of the order of 1021 cm2 s−1, only one order of magnitude larger than that of the Sun-Jupiter system.

A study of the Chamaeleon dark cloud and T-association - I. Extinction, distance and membership

We present the results of an observing programme to investigate the nature and degree of reddening of a number of stars in the field towards the dark cloud and T-association in Chamaeleon. The observations comprise optical (UBVRI) and infrared (JHK) photometry, and optical spectroscopy. New and previously published data are combined to assess membership criteria for 110 stars, and separate catalogues of association members and field stars are presented. Optical identifications are listed for 27 IRAS point sources in the region. The reddening/ distance relation for field stars indicates a distance to the cloud of 140±12 pc. This result confirms that the extinction law is anomalous towards some stars in the cloud, notably the embedded A0 ZAMS star HD 97300, with values of up to 5.5 for the ratio of total-to-selective extinction. A comparison of 21-cm data with the reddening of background field stars indicates that the ratio N(HI)/ E(B–V) is significantly less than the interstellar mean, indicating that most of the hydrogen in the cloud is molecular.

A study of the Chamaeleon dark cloud complex: survey, structure and embedded sources

A study of the Chamaeleon dark cloud complex: survey, structure and embedded sources

Photometric study of the Chamaeleon T-association

Optical and infrared photometry was carried out for a large sample of stars in the Chamaeleon dark cloud complex. The distance derived for the complex is 115 pc which makes it the nearest known dark cloud. A study of the stellar population contained within the cloud reveals a wide range of types ranging from a main-sequence A0 star to a large number of Orion population objects. The Chamaeleon complex may represent a stellar cluster intermediate in character between a T-association and an OB-association. The reddening law derived for this dark cloud suggests a value of R, the ratio of total-to-selective extinction, of 5.5; this result is similar to that found for other high gas and dust density regions. An HR diagram was constructed after correcting the observed stellar spectral energy distributions for the effects of reddening and circumstellar emission. The resulting diagram suggests a wide spread in stellar formation time. Finally, the optical and IR emission characteristics of the circumstellar envelopes are outlined briefly.