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Post Info TOPIC: Galaxy DDO 68
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DDO 68
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Title: Extremely metal-poor galaxy DDO 68: the LBV, H-alpha shells and the most luminous stars
Author: S.A. Pustilnik, L.N. Makarova, Y.A. Perepelitsyna, A.V. Moiseev, D.I. Makarov

The paper presents new results of the ongoing study of the unusual Lynx-Cancer void galaxy DDO 68 with record-low-metallicity regions (12+log(O/H) ~7.14) of the current star formation (SF). They include: a) a new spectrum and photometry with the 6-m SAO RAS telescope (BTA) for the Luminous Blue Variable (LBV = DDO68-V1). Photometric data sets are complemented with those based on the Sloan Digital Sky Survey (SDSS) and the Hubble Space Telescope (HST) archive images; b) the analysis of the DDO~68 supergiant shell (SGS) and the prominent smaller H-alpha arcs/shells visible at the HST image coupled with kinematics maps in H-alpha obtained with the Fabry-Perot interferometer (FPI) at the BTA; c) the list of identified at the HST images of about 50 most luminous stars (-9.1 < M_V < -6.0 mag) related to star-forming regions with the known extremely low O/H. This is intended to pave the path for the actual science with the next generation of giant telescopes. We confirm the earlier hints on significant variations of the LBV optical light deriving its amplitude of dV > 3.7~mag for the first time. New data suggest that in 2008--2010 the LBV reached M_V = --10.5 and probably underwent a giant eruption. We argue that the structure of star-forming complexes along the SGS (`Northern Ring') perimeter provides evidence for the sequential induced SF episodes caused by the shell gas instabilities and gravitational collapse. The variability of some DDO~68 luminous extremely metal-poor stars can be monitored with medium-size telescopes at sites with superb seeing.

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RE: Galaxy DDO 68
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Hubble snaps what looks like a young galaxy in the local Universe

Astronomers usually have to peer very far into the distance to see back in time, and view the Universe as it was when it was young. This new NASA/ESA Hubble Space Telescope image of galaxy DDO 68, otherwise known as UGC 5340, was thought to offer an exception. This ragged collection of stars and gas clouds looks at first glance like a recently-formed galaxy in our own cosmic neighbourhood. But, is it really as young as it looks?
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Title: Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68
Author: John M. Cannon, Megan Johnson, Kristen B.W. McQuinn, Erik D. Alfvin, Jeremy Bailin, H. Alyson Ford, Léo Girardi, Alec S. Hirschauer, Steven Janowiecki, John J. Salzer, Angela Van Sistine, Andrew Dolphin, E.C. Elson, Baerbel Koribalski, Paola Marigo, Jessica L. Rosenberg, Philip Rosenfield, Evan D. Skillman, Aparna Venkatesan, Steven R. Warren

We present HI spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only 3% solar luminosity, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (MHI = 2.8 x 10^7 solar masses), recently star-forming (SFRFUV = 1.4 x 10^-3 solar masses yr^-1, SFRH < 7^ x 10^-5 solar masses yr^-1) companion has the same systemic velocity as DDO 68 (Vsys = 506 km s^-1; D = 12.74±0.27 Mpc) and is located at a projected distance of 42 kpc. New HI maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness HI gas forms a bridge between these objects.

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Title: Discovery of a massive variable star with Z=Zo/36 in the galaxy DDO 68
Authors: S. A. Pustilnik (1), A. L. Tepliakova (1), A. Y. Kniazev (2 and 1), A. N. Burenkov (1) ((1) Special Astrophysical Observatory RAS, Russia, (2) SAAO, South Africa)

The Local Volume dwarf galaxy DDO 68, from the spectroscopy of its two brightest HII regions (Knots 1 and 2) was designated as the second most metal-poor star-forming galaxy [12+log(O/H)=7.14]. In the repeated spectral observations in 2008 January with the 6-m telescope (BTA) of the HII region Knot 3 [having 12+log(O/H)=7.10+-0.06], we find a strong evidence of a transient event related to a massive star evolution. From the follow-up observation with the higher spectral resolution in 2008 February, we confirm this phenomenon, and give parameters of its emission-line spectrum comprising of Balmer HI and HeI lines. The luminosities of the strongest transient lines (Ha, Hb) are of a few 10^36 erg s^-1. We also detected an additional continuum component in the new spectrum of Knot 3, which displays the spectral energy distribution raising to ultraviolet. The estimate of the flux of this continuum leads us to its absolute V-band magnitude of ~-7.1. Based on the spectral properties of this transient component, we suggest that it is related to an evolved massive star of luminous blue variable type with Z=Zo/36. We briefly discuss observational constraints on parameters of this unique (in the aspect of the record low metallicity of the progenitor massive star) event and propose several lines of its study.

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