arXiv subjects

M. G. Richer

Publications and source records attributed to M. G. Richer.

43 records · Page 3Linked to original sources

arXiv2005

On the most metal-poor PN and its binary central star

PN G135.9+55.9 is the most metal-poor PN known in our Galaxy. The central star resides in a short-period binary system with a compact component, probably a white dwarf. We describe new observations, which allowed us to determine the orbital period. The lower limit for the combined mass of both stars is close to the Chandrasekhar limit for white dwarfs, making this binary a possible progenitor of a supernova type Ia. The binary system must have recently emerged from a common envelope phase.

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arXiv2005

The kinematics of the large western knot in the halo of the young planetary nebula NGC 6543

A detailed analysis is presented of the dominant ionised knot in the halo of the planetary nebula NGC 6543. Observations were made at high spectral and spatial resolution of the [OIII] 5007 line using the Manchester echelle spectrometer combined with the 2.1-m San Pedro Martir Telescope. A 20-element multislit was stepped across the field to give almost complete spatial coverage of the knot and surrounding halo. The spectra reveal, for the first time, gas flows around the kinematically inert knot. The gas flows are found to have velocities comparable to the sound speed as gas is photo-evaporated off an ionised surface. No evidence is found of fast wind interaction with the knot and we find it likely that the fast wind is still contained in a pressure-driven bubble in the core of the nebula. This rules out the possibility of the knot having its origin in instabilities at the interface of the fast and AGB winds. We suggest that the knot is embedded in the slowly expanding Red Giant wind and that its surfaces are being continually photoionised by the central star.

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arXiv2004

A close binary nucleus in the most oxygen-poor planetary nebula PN G 135.9+55.9

We report FUSE and new deep optical spectroscopic observations of PN G 135.9+55.9, the most oxygen-poor planetary nebula located in the Galactic halo. These observations allow us to estimate the gravity of the central star by fitting the profile of the observed H I absorption lines with NLTE model atmospheres. Our best fit implies that the central star is still in a pre-white dwarf stage. We also find large variability of the radial velocities of the absorption component of the Balmer lines on a timescale of hours. This is direct evidence that the nucleus of PN G 135.9+55.9 is a close binary. The large semi-amplitude of the radial velocity variations and the probably short period suggest a massive compact companion, likely a white dwarf. Although our orbital solutions are very preliminary, they indicate that the total mass of the system probably exceeds the Chandrasekhar limit. If confirmed, this would make this binary the potential progenitor of a type Ia supernova.

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arXiv2003

The kinematics of the most oxygen-poor planetary nebula PN G135.9+55.9

PN G135.9+55.9 is a compact, high excitation nebula that has been identified recently as the most oxygen-poor halo planetary nebula. Given its very peculiar characteristics and potential implications in the realms of stellar and Galactic evolution, additional data are needed to firmly establish its true nature and evolutionary history. Here we present the first long-slit, high spectral resolution observations of this object in the lines of H$α$ and He II 4686. The position-velocity data are shown to be compatible with the interpretation of PN G135.9+55.9 being a halo planetary nebula. In both emission lines, we find the same two velocity components that characterize the kinematics as that of an expanding elliptical envelope. The kinematics is consistent with a prolate ellipsoidal model with axis ratio about 2:1, a radially decreasing emissivity distribution, a velocity distribution that is radial, and an expansion velocity of 30 km/s for the bulk of the material. To fit the observed line profiles, this model requires an asymmetric matter distribution, with the blue-shifted emission considerably stronger than the red-shifted emission. We find that the widths of the two velocity components are substantially wider than those expected due to thermal motions, but kinematic structure in the projected area covered by the slit appears to be sufficient to explain the line widths. The present data also rule out the possible presence of an accretion disk in the system that could have been responsible for a fraction of the H$α$ flux, further supporting the planetary nebula nature of PN G135.9+55.9.

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arXiv2002

Is HCG31 undergoing a merger or a fly-by interaction?

We present Fabry-Perot and multi-object spectroscopy of the galaxies in Hickson compact group 31 (HCG31). Based upon our H$α$ data cubes, galaxies A and C are a single entity, showing no discontinuity in their kinematics. Kinematically, galaxy E is probably a component of the A+C complex; otherwise it is a recently detached fragment. Galaxy F appears, both kinematically and chemically, to have formed from material tidally removed from the A+C complex. Galaxies B and G are kinematically distinct from this complex. Galaxy Q also has a radial velocity compatible with group membership. Galaxies A, B, C, and F have nearly identical oxygen abundances, despite spanning a luminosity range of 5$ $mag. Galaxy B's oxygen abundance is normal for its luminosity, while galaxy F's abundance is that expected given its origin as a tidal fragment of the A+C complex. The oxygen abundances in galaxies A and C are also understandable if the A+C complex is a late-type spiral suffering strong gas inflow and star formation as a result of a tidal interaction. Given the kinematics of both the galaxies and the \ion{H}{i} gas, the oxygen abundances, and the position of galaxy G, we propose that an interaction of galaxy G with the A+C complex, rather than a merger of galaxies A and C, is a more complete explanation for the tidal features and other properties of HCG31. In this case, the A+C complex need not be a merger in progress, though this is not ruled out.

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arXiv2002

The alpha-element abundances in the most oxygen-poor planetary nebula PN G 135.9+55.9

We present extensive new spectroscopy and imaging of PN G 135.9+55.9. We use these data as constraints to photoionization models to derive limits on the oxygen abundance. We find that PN G 135.9+55.9 has an oxygen abundance less than 1/50 of the solar value. Our models favour a value of 12 + \log O/H between 5.8 and 6.5 dex, confirming that PN G 135.9+55.9 is the most oxygen-poor planetary nebula known (Tovmassian et al. 2001). We also derive Ne/O = 0.5 +/- 0.3, S/O < 0.094, and Ar/O < 0.23. Although the value of Ne/O is nominally high, it need not imply that the progenitor of PN G 135.9+55.9 converted any of its initial oxygen abundance to neon. The helium abundance appears to be very low, He/H ~ 0.08, but a precise determination will require a much more detailed study. We find that Ha/Hb is lower than expected and perhaps variable, a finding for which we have no clear explanation.

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arXiv2001

IC 10: More evidence that it is a blue compact dwarf

We present optical spectroscopy of H {\sc ii} regions in the Local Group galaxy IC 10 and $UBVR$ photometry of foreground stars in three fields towards this galaxy. From these data, we find that the foreground reddening due to the Milky Way is $E(B-V)=0.77\pm 0.07 \mathrm{mag}$. We find that IC 10 contains considerable internal dust, which qualitatively explains the variety of reddening values found by studies of its different stellar populations. Based upon our foreground reddening, IC 10 has intrinsic photometric properties like those of a blue compact dwarf galaxy, and not those of a dwarf irregular. This result is consistent with much evidence that IC 10 is in the throes of a starburst that began at least $10 \mathrm{Myr}$ ago. We also report the discovery of a new WR star in the H {\sc ii} region HL111c.

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