Polarimetric Differential Imaging of the Class I Protostar

We present near-IR Adaptive Optics (AO) dual polarimetric observations of Elias 2–29, a Class I protostar in the Rho Ophiuchi star forming region. The main goal of these observations is to analyze the close environment of Elias 2–29 in order to derive the properties of its circumstellar disk and envelope. Elias 2–29 is known to be surrounded by circumstellar material (e.g. Boogert et al. 2000). Its spectral energy distribution (SED) has been studied in detail and it can be explained by the presence of a disk and an envelope. Mid-IR and radio observations suggest a disk inclination closer to face-on ( 60° Boogert et al. 2002). Higher spatial resolution observations of Elias 2–29 show diffuse emission around the target (Brandner et al. 2000). In spite of the brightness of the central object, the near-IR images reveal a bipolar reflection nebula and a dust lane in the NE-SW direction. This result is consistent with a high inclination of the system (see Figure 1). We have studied more in detail the vicinity of Elias 2– 29 through diffraction-limited observations. The observations were obtained at the Very Large Telescope (VLT/Paranal) combining AO and near-IR dual-imaging polarimetry techniques. The data were collected with the Nasmyth Adaptive Optics System (NAOS) and the infrared detector CONICA. NAOS is equipped with an infrared wavefront sensor (WFS) that allows observations of young stellar objects deeply embedded in their parental clouds. Elias 2–29 is a very bright object in the near-IR ( ), so we use it as a reference star with the IR WFS. The observations were performed with the Wollaston prism and different Hand K-band filters. We acquired images with short and long exposure times in order to analyze the inner and outer regions around Elias 2–29, respectively. We took exposures at four different rotator angles (0, 45, 90 and 135) and build the Stokes vectors (Q&U) combining the information of the different datasets. The K-band Qand U-intensity images of Elias 2–29 are displayed in Figure 2. We detect polarized light down to 1.5 ” from the central source, that is, down to 210 AU assuming a distance of 140 pc to the source. The total polarized signal ( ) is shown in the right panel of the figure. We clearly detect a dark lane in the NE–SW direction at an inclination of 30° (as in the ISAAC image). The highest polarized signal is located at both sides of the dark lane and perpendicular to it. The polarized emission is very symmetric in the vicinity of the source (radius 0.5 ”). At bigger radii, the polarized signal shows a ’spiral-like’ structure being more diffuse and extended in the SE direction and more compact and brighter in the NW direction. Khanzadyan et al. (2004) have performed an unbiased search for molecular hydrogen emission (H 1-0 S(1), 2.12 m) in the Rho Oph star forming region. The main goal of their study was to detect shock-excited knots and jets from young stellar objects. Elias 2–29 was among their observed targets and their deep H image is displayed in Figure 3. This figure E N ISAAC HK image