Point source

About: Point source is a research topic. Over the lifetime, 5077 publications have been published within this topic receiving 94091 citations.

Spitzer-IRAC GLIMPSE of high mass protostellar objects. I Infrared point sources and nebulae

Abstract: Aims. We conduct a statistical study of candidate massive protostellar objects in the 3.6–8.0 μ m bands of the Spitzer Space Telescope.Methods. The GLIMPSE archive was used to obtain 3.6–8.0 μ m point source photometry and images for 381 massive protostellar candidates lying in the Galactic midplane. The colours, magnitudes, and spectral indices of sources in each of the 381 target fields were analysed, and compared with the predictions of 2D radiative transfer model simulations. Results. Infrared point sources with intrinsic reddening were found associated with several massive protostars. Although no discernable embedded clusters were found in any targets, multiple sources or associations of reddened young stellar objects were found in many sources, indicating multiplicity at birth. The spectral index (α ) of these point sources in 3.6–8.0 μ m bands display high values of α = 2-5. A colour–magnitude analog plot was used to identify 79 infrared counterparts to the HMPOs that are bright at 8 μ m , centred on millimetre peaks, and that display α values in excess of 2. Compact nebulae are found in 75% of the detected sources with morphologies that can be described well by core-halo, cometary, shell-like, and bipolar geometries similar to those observed in ultra-compact HII regions.Conclusions. The IRAC band spectral energy distributions (SED) of the infrared counterparts of massive protostellar candidates are best described as representing YSOs with a mass range of 8–20 in their Class I evolutionary stages when compared with 2D radiative transfer models. They also suggest that the high α values represent reprocessed star/star+disk emission that is arising in the dense envelopes. Thus we are witnessing the luminous envelopes around the protostars rather than their photospheres or disks. We argue that the compact infrared nebulae very likely reflect the underlying physical structure of the dense cores and are found to imitate the morphologies of known UCHII regions. The observations are consistent with a scenario where massive protostars have formed inside dense cores and continue to accrete matter. Our results favour models of continuuing accretion involving both molecular and ionised accretion components to build the most massive stars rather than purely molecular, rapid accretion flows.

SPIRE point source photometry: within the Herschel interactive processing environment (HIPE)

Abstract: The different algorithms appropriate for point source photometry on data from the SPIRE instrument on-board the Herschel Space Observatory, within the Herschel Interactive Processing Environment (HIPE) are compared. Point source photometry of a large ensemble of standard calibration stars and dark sky observations is carried out using the 4 major methods within HIPE: SUSSEXtractor, DAOphot, the SPIRE Timeline Fitter and simple Aperture Photometry. Colour corrections and effective beam areas as a function of the assumed source spectral index are also included to produce a large number of photometric measurements per individual target, in each of the 3 SPIRE bands (250, 350, 500μm), to examine both the accuracy and repeatability of each of the 4 algorithms. It is concluded that for flux densities down to the level of 30mJy that the SPIRE Timeline Fitter is the method of choice. However, at least in the 250 and 350μm bands, all 4 methods provide photometric repeatability better than a few percent down to at approximately 100mJy. The DAOphot method appears in many cases to have a systematic offset of ∼8 % in all SPIRE bands which may be indicative of a sub-optimal aperture correction. In general, aperture photometry is the least reliable method, i.e. largest scatter between observations, especially in the longest wavelength band. At the faintest fluxes, <30mJy, SUSSEXtractor or DAOphot provide a better alternative to the Timeline Fitter.

A novel multifrequency technique for the detection of point sources in cosmic microwave background maps

Abstract: In this work we address the problem of simultaneous multifrequency detection of extragalactic point sources in the maps of the cosmic microwave background We apply a new linear filtering technique, the ‘matched matrix filters’, that incorporates full spatial information, including the cross-correlation among channels, without making any a priori assumption about the spectral behaviour of the sources A substantial reduction of the background is achieved thanks to the optimal combination of filtered maps We describe the new technique in detail and apply it to the detection of radio sources and estimation of their parameters in realistic all-sky Planck simulations at 30, 44, 70 and 100 GHz Then, we compare the results with the single-frequency approach based on the standard matched filter, in terms of reliability, completeness and flux accuracy of the resulting point source catalogues The new filters outperform the standard matched filters for all these indexes at 30, 44 and 70 GHz, whereas at 100 GHz both kinds of filters have a similar performance We find a notable increment of the number of true detections for a fixed reliability level In particular, for a 95 per cent reliability we practically double the number of detections at 30, 44 and 70 GHz

Quantification of bioluminescence images of point source objects using diffusion theory models

Abstract: A simple approach for estimating the location and power of a bioluminescent point source inside tissue is reported. The strategy consists of using a diffuse reflectance image at the emission wavelength to determine the optical properties of the tissue. Following this, bioluminescence images are modelled using a single point source and the optical properties from the reflectance image, and the depth and power are iteratively adjusted to find the best agreement with the experimental image. The forward models for light propagation are based on the diffusion approximation, with appropriate boundary conditions. The method was tested using Monte Carlo simulations, Intralipid tissue-simulating phantoms and ex vivo chicken muscle. Monte Carlo data showed that depth could be recovered within 6% for depth 4-12 mm, and the corresponding relative source power within 12%. In Intralipid, the depth could be estimated within 8% for depth 4-12 mm, and the relative source power, within 20%. For ex vivo tissue samples, source depths of 4.5 and 10 mm and their relative powers were correctly identified.