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تسجيل مستخدم جديدOn the distance and reddening of the starburst galaxy IC10
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We present deep and accurate optical photometry of the Local Group starburst galaxy IC10. The photometry is based on two sets of images collected with the Advanced Camera for Surveys and with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We provide new estimates of the Red Giant Branch tip (TRGB) magnitude, m_{F814W}^{TRGB}=21.90+-0.03, and of the reddening, E(B-V)=0.78+-0.06, using field stars in the Small Magellanic Cloud (SMC) as a reference. Adopting the SMC and two globulars, Omega Centauri and 47 Tucanae, as references we estimate the distance modulus to IC10: independent calibrations give weighted average distances of mu=24.51+-0.08 (TRGB) and mu=24.56+-0.08 (RR Lyrae). We also provide a new theoretical calibration for the TRGB luminosity, and using these predictions we find a very similar distance to IC10 (mu~24.60+-0.15). These results suggest that IC10 is a likely member of the M31 subgroup.
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We estimate the reddening and distance of the nearest starburst galaxy IC 10 using deep near infrared $JHK_{S}$ photometry obtained with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru telescope. We estimate the foreground re
ddening toward IC 10 using $UBV$ photometry of IC 10 from the Local Group Survey, obtaining $E(B-V)=0.52pm 0.04$ mag. We derive the total reddening including the internal reddening, $E(B-V)=0.98pm 0.06$ mag, using $UBV$ photometry of early-type stars in IC 10 and comparing $JHK_{S}$ photometry of red giant branch stars in IC 10 and the SMC. Using the 2MASS point source catalog of 20 Galactic globular clusters, we derive a relation between the metallicity [Fe/H]$_{CG97}$ and the slope of the red giant branch in the $K_{S}- (J-K_{S})$ color-magnitude diagram. The mean metallicity of the red giant branch stars in IC 10 is estimated to be [Fe/H]$_{CG97}=-1.08pm0.28$. The magnitude of the tip of the red giant branch (TRGB) of IC 10 in the $K_{S}$ band is measured to be $K_{S,TRGB}=18.28pm0.01$. Based on the TRGB method, we estimate the distance modulus of IC 10 to be $(m-M)_{0}=24.27pm0.03{rm (random)}pm0.18{rm (systematic)}$, corresponding to the distance of $d=715pm10pm60$ kpc. This confirms that IC 10 is a member of the Local Group.
We aim to explore whether strong magnetic fields can be effectively generated in low-mass dwarf galaxies and, if so, whether such fields can be affected by galactic outflows and spread out into the intergalactic medium (IGM). We performed a radio con
tinuum polarimetry study of IC10, the nearest starbursting dwarf galaxy, using a combination of multifrequency interferometric (VLA) and single-dish (Effelsberg) observations. VLA observations at 1.43 GHz reveal an extensive and almost spherical radio halo of IC10 in total intensity, extending twice more than the infrared-emitting galactic disk. The halo is magnetized with a magnetic field strength of 7 microG in the outermost parts. Locally, the magnetic field reaches about 29 microG in HII complexes, becomes more ordered, and weakens to 22 microG in the synchrotron superbubble and to 7-10 microG within HI holes. At the higher frequency of 4.86 GHz, we found a large-scale magnetic field structure of X-shaped morphology, similar to that observed in several edge-on spiral galaxies. The X-shaped magnetic structure can be caused by the galactic wind, advecting magnetic fields injected into the interstellar medium by stellar winds and supernova explosions. The radio continuum scale heights at 1.43 GHz indicate the bulk speed of cosmic-ray electrons outflowing from HII complexes of about 60 km/s, exceeding the escape velocity of 40 km/s. Hence, the magnetized galactic wind in IC10 inflates the extensive radio halo visible at 1.43 GHz and can seed the IGM with both random and ordered magnetic fields. These are signatures of intense material feedback onto the IGM, expected to be prevalent in the protogalaxies of the early Universe.
We present a photometric estimation of the distance and reddening values to the dwarf irregular galaxy NGC 1156, which is one of the best targets to study the isolated dwarf galaxies in the nearby universe. We have used the imaging data sets of the H
ubble Space Telescope (HST) Advanced Camera for Surveys (ACS) High Resolution Channel (HRC) of the central region of NGC 1156 (26 X 29) available in the HST archive for this study. From the (U-B, B-V) color-color diagram, we first estimate the total (foreground + internal) reddening toward NGC 1156 of E(B-V) =0.35 +/- 0.05 mag, whereas only the foreground reddening was previously known to be E(B-V)=0.16 mag (Burstein & Heiles) or 0.24 mag (Schlegel, Finkbeiner, & Davis). Based on the brightest stars method, selecting the three brightest blue supergiant (BSG) stars with mean B magnitude of <B(3B)> = 21.94 mag and the three brightest red supergiant (RSG) stars with mean V magnitude of <V(3R)> = 22.76 mag, we derive the distance modulus to NGC 1156 to be (m-M)_{0,BSG} = 29.55 mag and (m-M)_{0,RSG} = 29.16 mag. By using weights of 1 and 1.5 for the distance moduli from using the BSGs and the RSGs, respectively, we finally obtain the weighted mean distance modulus to NGC 1156 (m-M)_0 = 29.39 +/- 0.20 mag (d = 7.6 +/- 0.7 Mpc), which is in very good agreement with the previous estimates. Combining the photometry data of this study with those of Karachentsev et al. gives smaller distance to NGC 1156, which is discussed together with the limits of the data.
Extensive optical and infrared photometry as well as low and high resolution spectroscopy are used as inputs in deriving robust estimates of the reddening, distance and nature of the progenitor of V838 Mon. The reddening is found to obey the R_V=3.1
law and amounts to (i) E(B-V)=0.86 from the interstellar NaI and KI lines, (ii) E(B-V)=0.88 from the energy distribution of the B3V component and (iii) E(B-V)=0.87 from the progression of extinction along the line of sight. The adopted E(B-V)=0.87(+/-0.01) is also the amount required by fitting the progenitor with theoretical isochrones of appropriate metallicity. The distance is estimated from (a) the galactic kinematics of the three components of the interstellar lines, (b) the amount of extinction vs the HI column density and vs the dust emission through the whole Galaxy in that direction, from (c) spectrophotometric parallax to the B3V companion, from (d) comparison of the observed color-magnitude diagram of field stars with 3D stellar population models of the Galaxy, from (e) comparison of theoretical isochrones with the components of the binary system in quiescence and found to be around 10 kpc. Pre-outburst optical and IR energy distributions show that the component erupting in 2002 was brighter and hotter than the B3V companion. The best fit is obtained for a 50,000 K source, 0.5 mag brighter than the B3V companion. Comparison with theoretical isochrones suggests an age of 4 million year for the system and a mass around 65 M(sun) for the progenitor of the outbursting component, which at the time of the outburst was approaching the Carbon ignition stage in its core. The 2002 event is probably just a shell thermonuclear event in the outer envelope of the star.
We report the results of spectroscopic observations, obtained with the Gemini North Multi-Object Spectrograph, of 9 planetary nebulae (PNe) and 15 hii regions located in the 5.5arcmin $times$5.5arcmin inner region of the nearby starburst galaxy IC10.
Twelve new candidate PNe have been discovered during our pre-imaging phase. Nine of them have been spectroscopically confirmed. The direct availability of the electron temperature diagnostics in several nebulae allowed an accurate determination of the metallicity map of IC10 at two epochs: the present-time from hii regions and the old/intermediate-age from PNe. We found a non-homogeneous distribution of metals at both epochs, but similar average abundances were found for the two populations. The derived age-metallicity relation shows a little global enrichment interpreted as the loss of metals by SN winds and to differential gas outflows. Finally, we analyzed the production of oxygen --through the third dredge-up-- in the chemical abundance patterns of the PN populations belonging to several dwarf irregular galaxies. We found that the third dredge-up of oxygen is a metallicity dependent phenomenon occurring mainly for 12+$log$(O/H)$leq$7.7 and substantially absent in IC10 PNe.
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