Bayesian Analysis of Many-Pole Fits of Hadron Propagators in Lattice QCD

We use Bayes' probability theorem to analyze many-pole fits of hadron propagators. An alternative method of estimating values and uncertainties of the fit parameters is offered, which has certain advantages over the conventional methods. The probability distribution of the parameters of a fit is calculated. The relative probability of various models is calculated.Comment: 4 pages, 6 figures, Latex with espcrc2.sty, uuencoded compressed tar file contains 7 Latex files: 1 with the paper and 6 with the figures. Talk presented at LATTICE96(spectrum

Spectral Density on the Lattice

Spectral density in the pseudoscalar and vector channels is extracted from the SU(2) lattice quenched data. It is shown to consist of three sharp poles within the energy range accessible on the lattice.Comment: 38 pages, uuencoded tar-compressed ps-fil

Filtering of Signal Dependent Noise Applied to MIPS Data

Linear filtering and usual nonlinear median filtering are not effective for signal-dependent noise removal. We apply here an approximate decoupling of signal and noise by means of a nonlinear transform. The transform is followed by a linear filter and the corresponding inverse transform. This procedure allows us to mitigate the signal-dependent noise in the images obtained by the Multiband Imaging Photometer for Spitzer (MIPS), 70μm imaging band

Spitzer 24-micron Time-Series Observations of the Eclipsing M-dwarf Binary GU Bootis

We present a set of {\it Spitzer} 24$\mu$m MIPS time series observations of the M-dwarf eclipsing binary star GU Bo\"otis. Our data cover three secondary eclipses of the system: two consecutive events and an additional eclipse six weeks later. The study's main purpose is the long wavelength (and thus limb darkening-independent) characterization of GU Boo's light curve, allowing for independent verification of the results of previous optical studies. Our results confirm previously obtained system parameters. We further compare GU Boo's measured 24$\mu$m flux density to the value predicted by spectral fitting and find no evidence for circumstellar dust. In addition to GU Boo, we characterize (and show examples of) light curves of other objects in the field of view. Analysis of these light curves serves to characterize the photometric stability and repeatability of {\it Spitzer's} MIPS 24\micron array over short (days) and long (weeks) timescales at flux densities between approximately 300--2,000$\mu$Jy. We find that the light curve root mean square about the median level falls into the 1--4% range for flux densities higher than 1mJy. Finally, we comment on the fluctuations of the 24\micron background on short and long timescales.Comment: ApJ accepted. 10 pages, 12 figure

The Spitzer Survey of the Small Magellanic Cloud: Discovery of Embedded Protostars in the HII Region NGC 346

We use Spitzer Space Telescope observations from the Spitzer Survey of the Small Magellanic Cloud (S3MC) to study the young stellar content of N66, the largest and brightest HII region in the SMC. In addition to large numbers of normal stars, we detect a significant population of bright, red infrared sources that we identify as likely to be young stellar objects (YSOs). We use spectral energy distribution (SED) fits to classify objects as ordinary (main sequence or red giant) stars, asymptotic giant branch stars, background galaxies, and YSOs. This represents the first large-scale attempt at blind source classification based on Spitzer SEDs in another galaxy. We firmly identify at least 61 YSOs, with another 50 probable YSOs; only one embedded protostar in the SMC was reported in the literature prior to the S3MC. We present color selection criteria that can be used to identify a relatively clean sample of YSOs with IRAC photometry. Our fitted SEDs indicate that the infrared-bright YSOs in N66 have stellar masses ranging from 2 Msun to 17 Msun, and that approximately half of the objects are Stage II protostars, with the remaining YSOs roughly evenly divided between Stage I and Stage III sources. We find evidence for primordial mass segregation in the HII region, with the most massive YSOs being preferentially closer to the center than lower-mass objects. Despite the low metallicity and dust content of the SMC, the observable properties of the YSOs appear consistent with those in the Milky Way. Although the YSOs are heavily concentrated within the optically bright central region of N66, there is ongoing star formation throughout the complex and we place a lower limit on the star formation rate of 3.2 x 10^-3 Msun/yr over the last ~1 Myr.Comment: 13 pages, 5 figures (3 in color), 2 tables. Accepted for publication in Ap

Expansion Aspect of Color Transparency on the Lattice

The opportunity to observe color transparency (CT) is determined by how rapidly a small-sized hadronic wave packet expands. Here we use SU(2) lattice gauge theory with Wilson fermions in the quenched approximation to investigate the expansion. The wave packet is modeled by a point hadronic source, often used as an interpolating field in lattice calculations. The procedure is to determine the Euclidean time (t), pion channel, Bethe-Salpeter amplitude $\Psi(r,t)$, and then evaluate $b^2(t)=\int d^3 r \Psi(r,t) r^2 sin^2 \theta \Psi_{\pi}(r)$. This quantity represents the soft interaction of a small-sized wave packet with a pion. The time dependence of $b^2(t)$ is fit as a superposition of three states, which is found sufficient to reproduce a reduced size wave packet. Using this superposition allows us to make the analytic continuation required to study the wave packet expansion in real time. We find that the matrix elements of the soft interaction $\hat b^2$ between the excited and ground state decrease rapidly with the energy of the excited state.Comment: 19 pages, latex, 4 figure

Characterizing star formation activity in infrared dark cloud MSXDC G048.65-00.29

Infrared Dark Clouds (IRDCs), condensed regions of the ISM with high column densities, low temperatures and high masses, are suspected sites of star formation. Thousands of IRDCs have already been identified. To date, it has not been resolved whether IRDCs always show star formation activity and, if so, if massive star formation (> 8 solar masses) is the rule or the exception in IRDCs. Previous analysis of sub-millimeter cores in the cloud MSXDC G048.65-00.29 (G48.65) indicates embedded star formation activity. To characterize this activity in detail, mid-infrared photometry (3-30 micron) has been obtained with the Spitzer Space Telescope. This paper analyzes the point sources seen in the 24 micron band, combined with counterparts or upper limits at shorter and longer wavelengths. Data points in wavelength bands ranging from 1 up to 850 micron are used to compare each 24 micron source to a set of Spectral Energy Distributions of Young Stellar Object (YSO) models. By assessing the models that fit the data, an attempt is made to identify YSOs as such and determine their evolutionary stages and stellar masses. A total of 17 sources are investigated, 13 of which are classified as YSOs, primarily - but not exclusively - in an early embedded phase of star formation. The modeled masses of the central stellar objects range from sub-solar to ~8 solar masses. Every YSO is at less than 1 pc projected distance from its nearest YSO neighbor. We conclude that IRDC G48.65 is a region of active star formation. We find YSOs in various evolutionary phases, indicating that the star formation in this cloud is not an instantaneous process. The inferred masses of the central objects suggest that this IRDC hosts only low to intermediate mass YSOs and none with masses exceeding ~8 solar masses.Comment: 10 pages, 6 figures; v2: minor editorial changes to match published versio

Galactic bulge giants: probing stellar and galactic evolution I. Catalogue of Spitzer IRAC and MIPS sources

Aims: We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods: To this end, we observed seven 15 times 15 arcmin^2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results: In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.Comment: 21 pages, accepted for publication in A&A. A version with high-resolution figures, as well as the data catalogues (including cross-id with GLIMPSE and GALCEN) and image mosaics are available at the anonymous ftp://ftp.ster.kuleuven.be/dist/stefan/Spitzer