* Astronomy

NGC 247 (also Caldwell 62, ESO 540-22, IRAS 00446-2101, MCG -4-3-5, UGCA 11 and PGC 2758) is a magnitude +9.9 intermediate spiral galaxy located 11.1 ±1.2 million light-years away in the constellation Cetus.

The galaxy was discovered by German-British astronomer William Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at Datchet, Berkshire, on the 20th October 1784.

Position (J2000): R.A. 00h 47m 08.5s  |  Dec. -20° 45' 37"

NGC 247 is marred by an unusually large void on one side of its spiral disk. This void contains some older, redder stars but no younger, bluer stars.
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Title: Chandra and HST Observations of the Supersoft ULX in NGC 247: Candidate for Standard Disk Emission
Authors: Lian Tao, Hua Feng, Philip Kaaret, Fabien Grisé, Jing Jin

We report on multiwavelength observations of the supersoft ultraluminous X-ray source (ULX) in NGC 247 made with the Chandra X-ray Observatory and Hubble Space Telescope (HST). We aligned the X-ray and optical images using three objects present on both and identified a unique, point-like optical counterpart to the ULX. The X-ray to optical spectrum is well fitted with an irradiated disk model if the extinction measured for Cepheids in NGC 247 is used. Assuming only Galactic extinction, then the spectrum can be modelled as a standard thin accretion disk. Either result leads to the conclusion that a disk interpretation of the X-ray spectrum is valid, thus the source may be in the X-ray thermal state and contain an intermediate mass black hole of at least 600 solar masses. In contrast to other supersoft ULXs which are transient and exhibit a luminosity temperature relation inconsistent with a disk interpretation of the X-ray emission, the NGC 247 ULX has a relatively steady flux and all available X-ray data are consistent with emission from a disk in the thermal state.

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Title: The Araucaria Project. The Distance to the Sculptor Galaxy NGC 247 from Near-Infrared Photometry of Cepheid Variables
Authors: W. Gieren, G. Pietrzynski, I. Soszynski, O. Szewczyk, F. Bresolin, R.-P. Kudritzki, M. Urbaneja, J. Storm, D. Minniti, A. Garcia-Varela

We have obtained deep near-infrared images in J and K filters of four fields in the Sculptor Group spiral galaxy NGC 247 with the ESO VLT and ISAAC camera. For a sample of ten Cepheids in these fields, previously discovered by Garcia-Varela et al. from optical wide-field images, we have determined mean J and K magnitudes and have constructed the period-luminosity (PL) relations in these bands. Using the near-infrared PL relations together with those in the optical V and I bands, we have determined a true distance modulus for NGC 247 of 27.64 mag, with a random uncertainty of ±2% and a systematic uncertainty of ~4% which is dominated by the effect of unresolved stars on the Cepheid photometry. The mean reddening affecting the NGC 247 Cepheids of E(B-V) = 0.18 ± 0.02 mag is mostly produced in the host galaxy itself and is significantly higher than what was found in the previous optical Cepheid studies in NGC 247 of our own group, and Madore et al., leading to a 7% decrease in the previous optical Cepheid distance. As in other studies of our project, the distance modulus of NGC 247 we report is tied to an assumed LMC distance modulus of 18.50. Comparison with other distance measurements to NGC 247 shows that the present IR-based Cepheid distance is the most accurate among these determinations.
With a distance of 3.4 Mpc, NGC 247 is about 1.5 Mpc more distant than NGC 55 and NGC 300, two other Sculptor Group spirals analysed before with the same technique by our group.

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