Astronomical instrumentation

Abstract:

We present new photometric and spectroscopic measurements for the unique, young, low-mass evolutionary track calibrator AB Dor C. While the new Ks photometry is similar to that previously published in Close et al. (2005) the spectral type is found to be earlier. Based on new H & K IFS spectra of AB Dor C (Thatte et al. 2007; paper 1) we adopt a spectral type of M5.5+/-1.0 for AB Dor C. This is considerably earlier than the M8+/-1 estimated in Close et al. (2005) and Nielsen et al. (2005) yet is consistent with the M6+/-1 independently derived by Luhman & Potter (2005). However, the spectrum presented in paper 1 and analyzed here is a significant improvement over any previous spectrum of AB Dor C. We also present new astrometry for the system which further supports a 0.090+/-0.005 Msun mass for the system. Once armed with an accurate spectrum and Ks flux we find L=0.0021+/-0.0005 Lsun and Teff=2925{+170}{-145}K for AB Dor C. These values are consistent with a ~75 Myr 0.090+/-0.005 Msun object like AB Dor C according to the DUSTY evolutionary tracks (Chabrier et al. 2000). Hence masses can be estimated from the HR diagram with the DUSTY tracks for young low-mass objects like AB Dor C. However, we cautiously note that underestimates of the mass from the tracks can occur if one lacks a proper (continuum preserved) spectra or is relying on NIR fluxes alone.

Abstract:

As the first part of a development programme on computer-guided alignment(CGA), we model the alignment influence on the optical wavefront in terms of the phase and amplitude modulation. This modulation is derived from the interaction between alignment parameters and influence functions, both expressed in complex form. The alignment influence model is used to approximate the ray-traced target wavefront of a randomly mis-aligned multi-element system. The approximated wavefront shows a factor of ∼ 100 improvement in predicting the target, when coupled non-linear influences among elements are included. This demonstrates the significance of the inter-element effect. We discuss the possibility of adopting the model for rectifying mis-alignment of multi-element systems. © 2007 Optical Society of America.

Abstract:

We present a detailed analysis of the spatially resolved properties of the lensed submillimeter galaxy (SMG) SMM J14011+0252 atz = 2.56, combining deep near-infrared integral-field data obtained with SPIFFI on the VLT with other multiwavelength data sets. As previously discussed by other authors, the broad characteristics of SMM J14011+0252 in particular and submillimeter galaxies in general are in agreement with what is expected for the early evolution of local massive spheroidal galaxies. From continuum and line flux, velocity, and dispersion maps, we measure the kinematics, star formation rates, gas densities, and extinction for individual subcomponents. The star formation intensity is similar to low-redshift "maximal starbursts," while the line fluxes and the dynamics of the emission line gas provide direct evidence for a starburst-driven wind with physical properties very similar to local superwinds. We also find circumstantial evidence for "self-regulated" star formation within J1. The relative velocity of the bluer companion J2 yields a dynamical mass estimate for J1 within ∼20 kpc of Mdyn ∼ 1 × 1011 M⊙. The relative metallicity of J2 is 0.4 dex lower than in J1n/J1s, suggesting different star formation histories. Spectral energy distribution fitting of the continuum peak J1c confirms and substantiates previous suggestions that this component is a z = 0.25 interloper. When removing J1c, the stellar continuum and Hα line emission appear well aligned spatially in two individual components, J1n and J1s, and coincide with two kinematically distinct regions in the velocity map, which might well indicate a merging system. This highlights the close similarity between SMGs and ultraluminous infrared galaxies (ULIRGs), which are often mergerdriven maximal starbursts, and suggests that the intrinsic mechanisms of star formation and related feedback are in fact similar to low-redshift strongly star-forming systems. © 2007. The American Astronomical Society. All rights reserved.