arXiv subjects
Publications and source records attributed to A. De Luca.
We present optical observations of the fields of two X-ray sources located near the center of the shell-like supernova remnant G266.1-1.2. No objects brighter than R~22.5 and B~23 are present within the small Chandra error region of AX J0851.9-4617.4, besides a R~17 star that has already been excluded as a possible counterpart. A bright diffuse H_alpha nebula is present close to the position of the candidate neutron star.
The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed to be 500 pc. Although affected by a significant uncertainty, this value stuck to both the pulsar and the SNR. In an effort to obtain a model free distance measurement, we have applied high resolution astrometry to the pulsar V~23.6 optical counterpart. Using a set of five HST/WFPC2 observations, we have obtained the first optical measurement of the annual parallax of the Vela pulsar. The parallax turns out to be 3.4 +/- 0.7 mas, implying a distance of 294(-50;+76) pc, i.e. a value significantly lower than previously believed. This affects the estimate of the pulsar absolute luminosity and of its emission efficiency at various wavelengths and confirms the exceptionally high value of the N_e towards the Vela pulsar. Finally, the complete parallax data base allows for a better measurement of the Vela pulsar proper motion (mu_alpha(cos(delta))=-37.2 +/- 1.2 mas/yr; mu_delta=28.2 +/- 1.3 mas/yr after correcting for the peculiar motion of the Sun) which, at the parallax distance, implies a transverse velocity of ~65 km/s. Moreover, the proper motion position angle appears specially well aligned with the axis of symmetry of the X-ray nebula as seen by Chandra. Such an alignment allows to assess the space velocity of the Vela pulsar to be ~81 km/s.
Given their intrinsic faintness, isolated neutron stars represent an elusive target for optical astronomy. Up to date, an optical counterpart has been identified only for a very tiny fraction of the overall population of more than 1000 radio pulsars. The HST contributions to the optical studies of isolated neutron stars have been recently reviewed by Mignani et al. (2000) and by Caraveo et al. (these proceedings). Here, we review its specific contribution in the field of pulsar astrometry and kinematics.
The quest for the distance of the Vela and Geminga pulsars yielded, so far, a set of four WFPC2 images for each object. The availability of couples of images taken at the same period of the year, thus affected by the same parallactic displacement, prompted us to use Vela and Geminga as test cases to assess the reliability of HST astrometry.
High resolution images of the Crab-like SNR SNR0540-69 have been recently obtained by the HRC, on board the Chandra X-ray Observatory, and by the FORS1 instrument, attached to ESO/VLT1. A detailed comparison of these images with an archival Planetary Camera one will be presented.
Using all the HST WFC/WFPC2 images of the field collected so far, we have performed an accurate relative astrometry analysis to re-assess the value of the Vela pulsar proper motion. Although covering a much shorter time span, our measurement clearly confirms the previous result obtained by Nasuti et al. (1997) using ground-based optical data and nails the proper motion value to mu = 52 +/- 3 mas/yr.
We have designed and built a large-throughput dual channel photometer, Diabolo. This photometer is dedicated to the observation of millimetre continuum diffuse sources, and in particular, of the Sunyaev-Zel'dovich effect and of anisotropies of the 3K background. We describe the optical layout and filtering system of the instrument, which uses two bolometric detectors for simultaneous observations in two frequency channels at 1.2 and 2.1 mm. The bolometers are cooled to a working temperature of 0.1 K provided by a compact dilution cryostat. The photometric and angular responses of the instrument are measured in the laboratory. First astronomical light was detected in March 1995 at the focus of the new Millimetre and Infrared Testa Grigia Observatory (MITO) Telescope. The established sensitivity of the system is of 7 mK_RJ s^1/2$. For a typical map of at least 10 beams, with one hour of integration per beam, one can achieve the rms values of y_SZ ~ 7 10^-5 and the 3K background anisotropy Delta T/T ~ 7 10^-5, in winter conditions. We also report on a novel bolometer AC readout circuit which allows for the first time total power measurements on the sky. This technique alleviates (but does not forbid) the use of chopping with a secondary mirror. This technique and the dilution fridge concept will be used in future scan--modulated space instrument like the ESA Planck mission project.
In order to assess the potential of future microwave anisotropy space experiments for detecting clusters by their Sunyaev-Zeldovich (SZ) thermal effect, we have simulated maps of the large scale distribution of their Compton parameter $y$ and of the temperature anisotropy $ΔT/T$ induced by their proper motion. Our model is based on a predicted distribution of clusters per unit redshift and flux density using a Press-Schecter approach. These maps were used to create simulated microwave sky by adding them to the microwave contributions of the emissions of our Galaxy and the primary Cosmic Microwave Background (CMB) anisotropies. In order to simulate measurements representative of what current technology should achieve, ``observations'' were performed according to the instrumental characteristics of the COBRAS/SAMBA space mission. We then analyzed the resulting $y$ and $ΔT/T$ maps which now include both the primary anisotropies and those superimposed due to cluster motions.
Here follows a preliminary report on the construction of fake millimeter and sub-millimeter skies, as observed by virtual instruments, e.g. the COBRA/SAMBA mission, using theoretical modeling and data extrapolations. Our goal is to create maps as realistic as possible of the relevant physical contributions which may contribute to the detected signals. This astrophysical modeling is followed by simulations of the measurement process itself by a given instrumental configuration. This will enable a precise determination of what can and cannot be achieved with a particular experimental configuration, and provide a feedback on how to improve the overall design. It is a key step on the way to define procedures for the separation of the different physical processes in the future observed maps. Note that this tool will also prove useful in preparing and analyzing current (\eg\ balloon borne) Microwave Background experiments. Keywords: Cosmology -- Microwave Background Anisotropies.