A New Galactic Extinction Map in High Ecliptic Latitudes

In this study, we derived a galactic extinction map in high ecliptic latitudes for |\beta| > 30 degrees. The dust temperature distribution was derived from the intensities at 100 and 140 \mu m with a spatial resolution of 5'. The intensity at 140 \mu m was derived from the intensities at 60 and 100 \mu m of the IRAS data assuming two tight correlations between the intensities at 60, 100, and 140 \mu m of the COBE/DIRBE data. We found that these correlations can be separated into two correlations by the antenna temperature of the radio continuum at 41 GHz. Because the present study can trace the 5'-scale spatial variation in the dust temperature distribution, it has an advantage over the extinction map derived by Schlegel, Finkbeiner, and Davis, who used the DIRBE maps to derive dust temperature distribution with a spatial resolution of 1 degrees. We estimated the accuracy of our method by comparing it with that of Schlegel, Finkbeiner, and Davis. The spatial resolution difference was found to be significant. The area in which the significant difference is confirmed occupies 28% of the region for |\beta| > 30 degrees. With respect to the estimation of extragalactic reddening, the present study has an advantage over the extinction map derived by Dobashi (2011), which was based on the 2MASS Point Source Catalog, because our extinction map is derived on the basis of far-infrared emission. Dobashi's extinction map exhibits a maximum value that is lower than that of our map in the galactic plane and a signal-to-noise ratio that is lower than that of our map in high galactic latitudes. This significant difference is confirmed in 81% of the region for |\beta| > 30 degrees. In the areas where the significant differences are confirmed, the extinction should be estimated using our method rather than the previous methods.Comment: 28 pages, 14 figures, accepted for publication in PAS

Modelling the Galactic bar using OGLE-II Red Clump Giant Stars

Red clump giant stars can be used as distance indicators to trace the mass distribution of the Galactic bar. We use RCG stars from 44 bulge fields from the OGLE-II microlensing collaboration database to constrain analytic tri-axial models for the Galactic bar. We find the bar major axis is oriented at an angle of 24 - 27 degrees to the Sun-Galactic centre line-of-sight. The ratio of semi-major and semi-minor bar axis scale lengths in the Galactic plane x_0, y_0, and vertical bar scale length z_0, is x_0 : y_0 : z_0 = 10 : 3.5 : 2.6, suggesting a slightly more prolate bar structure than the working model of Gerhard (2002) which gives the scale length ratios as x_0 : y_0 : z_0 = 10 : 4 : 3 .Comment: 15 pages, 10 figures, accepted for publication in MNRAS. Supplementary material available online: 10 pages, 10 figure

Study of infrared excess from circumstellar disks in binaries with Spitzer/IRAC

The presence of excess emission at 3.6--8.0 $\mu$m was investigated in a sample of 27 binary systems located in two nearby star-forming regions, Taurus and Ophiuchus, by using Spitzer/Infrared Array Camera (IRAC) archival data. Angular (Projected) separations for the binaries are greater than 2"($\sim$280 AU), which allowed us to perform spatially resolved photometry of individual primary and secondary sources. The measured occurrence of infrared excess suggests that binarity plays a role in the evolution of circumstellar disks, even at such wide binary separations. Most of the binaries have excess emission from both the circumprimary and circumsecondary disks, or show photospheric levels for both components at all four wavelengths of IRAC. On the other hand, four systems ($17^{+11}_{-8}$%, designated by "mixed" systems) exhibit excess emission from a single binary component. This ratio is significantly smaller than that predicted by the random pairing of single stars, suggesting that circumprimary and circumsecondary disks are synchronously dispersed. In addition, the excess frequencies (EFs) of primary and secondary sources with a projected distance of $a_{\rm p}$$\simeq$280--450 AU are $100^{+0}_{-17}$% and $91^{+8}_{-18}$%, respectively, and significantly higher than that of single stars ($70 \pm 5$%). We made a simple model describing the EF distribution as a function of the disk outer radius, $R_{\rm out}$. Comparisons with observations using the Kolmogorov-Smirnov test show that the observational data are consistent with the model when the $\rm{EF} \simeq 1$ region is found at $R_{\rm out}$$\sim$30--100 AU. This disk radius is smaller than that typically estimated for single stars. The high EF of circumstellar disks with these radii may indicate a prolonged lifetime of dust in binary systems possibly because smaller disks counteract mass loss by photoevaporation.Comment: 29 pages, 10 figures, accepted for publication in PAS

Constraining the Location of Microlensing Objects by using the Finite Source Effect in EAGLE events

We propose a new method to constrain the location of microlensing objects using EAGLE (Extremely Amplified Gravitational LEnsing) events. We have estimated the rate of EAGLE events by taking the finite-source effect in to account. We found that the EAGLE event rate for using a 1-m class telescope w hose limiting magnitude is $V \sim 21$ is the same as or higher than that of the ordinary microlensing events which have been found to date. We have also found that the fraction of transit EAGLE events is large enough to detect: between $4 \sim 80$ depending on the lens location. Since the lens proper motion can be measured for a transit event, one can distinguish whether the lens is a MACHO (MAssive Compact Halo Object) in our hal o or one of the known stars in the Large Magellanic Cloud (LMC) from the proper motion measurement for each transit EAGLE event. Moreover, we show that the fraction of transit EAGLEs in all EAGLE events signif icantly depends on the lensing locations: the transit EAGLE fraction for the sel f-lensing case is $2 \sim 15$ times larger than that for halo MACHOs. Thus, one can constrain the location of lens objects by the statistics of the tr ansit events fraction. We show that we can reasonably expect $0 \sim 6$ transit events out of 21 EAGLE events in 3 years. We can also constrain the lens population properties at a gre ater than 99% confidence level depending on the number of transit events de tected. We also present the duration of EAGLE events, and show how an hourly ob servational mode is more suitable for an EAGLE event search program.Comment: 18 pages, 4 figures, accepted for publication in Ap

Proper Motion Dispersions of Red Clump Giants in the Galactic Bulge: Observations and Model Comparisons

Red clump giants in the Galactic bulge are approximate standard candles and hence they can be used as distance indicators. We compute the proper motion dispersions of RCG stars in the Galactic bulge using the proper motion catalogue from the second phase of the Optical Gravitational Microlensing Experiment (OGLE-II, Sumi et al. 2004) for 45 fields. The proper motion dispersions are measured to a few per cent accuracy due to the large number of stars in the fields. The observational sample is comprised of 577736 stars. These observed data are compared to a state-of-the-art particle simulation of the Galactic bulge region. The predictions are in rough agreement with observations, but appear to be too anisotropic in the velocity ellipsoid. We note that there is significant field-to-field variation in the observed proper motion dispersions. This could either be a real feature, or due to some unknown systematic effect.Comment: 12 pages, 13 figures, accepted for publication in MNRA

Extinction Map of the Galactic center: OGLE-II Galactic bulge fields

We present the reddening (E(V-I)) and Extinction maps in V-band (A_V) and I-band (A_I) for 48 Optical Gravitational Lensing Experiment II (OGLE-II) Galactic bulge (GB) fields, covering a range of $-11^\circ <l< 11^\circ$, with the total area close to 11 square degrees. These measurements are based on two-band photometry of Red Clump Giant (RCG) stars in OGLE-II VI maps of GB. We confirm the anomalous value of the ratio of total to selective extinction $R_{VI} = A_V / E(V-I) = 1.9 \sim 2.1$, depending on the line of sight, as measured by Udalski (2003). By using the average value of $R_{VI}=1.964$ with the standard deviation sdev=0.085, we measured E(V-I), A_V and A_I, and we obtained extinction and reddening maps with a high spatial resolution of $26.7''\sim 106.8''$, depending on the stellar density of each field. We assumed that average, reddening corrected colours of red clump giants are the same in every field. The maps cover the range 0.42<E(V-I)<3.5, 0.83<A_V<6.9 and 0.41<A_I<3.4 mag respectively. The zero points of these maps are calibrated by using V-K colours of 20 RR Lyrae ab variables (RRab) in Baade's window. The apparent reddening corrected I-band magnitudes of the RCGs change by +0.4 mag while the Galactic coordinate l varies from $+5^{\circ}$ to $-5^{\circ}$, indicating that these stars are in the Galactic Bar. The reddening corrected colour of RRab and RCGs in GB are consistent with colours of local stars, while in the past these colours were claimed to be different.Comment: 13 pages, 15 figures, Accepted for publication in MNRA

Blending in Gravitational Microlensing Experiments: Source Confusion And Related Systematics

Gravitational microlensing surveys target very dense stellar fields in the local group. As a consequence the microlensed source stars are often blended with nearby unresolved stars. The presence of `blending' is a cause of major uncertainty when determining the lensing properties of events towards the Galactic centre. After demonstrating empirical cases of blending we utilize Monte Carlo simulations to probe the effects of blending. We generate artificial microlensing events using an HST luminosity function convolved to typical ground-based seeing, adopting a range of values for the stellar density and seeing. We find that a significant fraction of bright events are blended, contrary to the oft-quoted assumption that bright events should be free from blending. We probe the effect that this erroneous assumption has on both the observed event timescale distribution and the optical depth, using realistic detection criteria relevent to the different surveys. Importantly, under this assumption the latter quantity appears to be reasonably unaffected across our adopted values for seeing and density. The timescale distribution is however biased towards smaller values, even for the least dense fields. The dominant source of blending is from lensing of faint source stars, rather than lensing of bright source stars blended with nearby fainter stars. We also explore other issues, such as the centroid motion of blended events and the phenomena of `negative' blending. Furthermore, we breifly note that blending can affect the determination of the centre of the red clump giant region from an observed luminosity function. This has implications for a variety of studies, e.g. mapping extinction towards the bulge and attempts to constrain the parameters of the Galactic bar through red clump giant number counts. (Abridged)Comment: 18 pages, 10 figures. MNRAS (in press