Anabel Arrieta

Non-Local Thermodynamic Equilibrium Model of NGC 6543’s Central Star and Its Relation to the Surrounding Planetary Nebula

We analyze the chemical composition of the central star of the planetary nebula NGC 6543 based on a detailed NLTE model of its stellar wind. The logarithmic abundances by number are H = 12.00, He = 11.00, C = 9.03, N = 8.36, O = 9.02, Si = 8.19, P = 5.53, S = 7.57, and Fe = 7.24. Compared with the solar abundances, most of the elements have solar composition with respect to hydrogen, except C, which is overabundant by 0.28 dex, and Fe, which is depleted by ~0.2 dex. Contrary to most previous work, we find that the star is not H-poor and has a normal He composition. These abundances are compared with those found in the diffuse X-ray plasma and the nebular gas. Compared to the plasma emitting in diffuse X-rays, the stellar wind is much less depleted in iron. Since the iron depletions in the nebular gas and X-ray plasma are similar, we conclude that the plasma emitting diffuse X-rays is derived from the nebular gas rather than the stellar wind. Excellent agreement is obtained between the abundances in the stellar wind and the nebular recombination line abundances for He, C, and O relative to H. On the other hand, the derived stellar N abundance is smaller than the nebular N abundance derived from recombination lines and agrees with the abundance found from collisionally excited lines. The mean temperature variation determined by five different methods indicates that the difference in the nebular abundances between the recombination lines and collisionally excited lines can be explained as due to the temperature variations in a chemically homogeneous medium.

The proto-planetary nebula M1-92 and the symbiotic star MWC 560 : Two evolutionary phases of the same type of object?

Important similarities between the objects M1-92, a proto-planetary nebula of bipolar morphology, and MWC 560, a symbiotic star with a jet, have been found. A brief review of the previous studies for both objects is presented for the purpose of proposing mechanisms that best explain these similarities, since up to now both objects have been studied independently. From the comparison of the spectra of both objects, the existence of a jet is confirmed for the proto-planetary nebula M1-92, as well as its binary nature and the existence of a circumnuclear disk. Finally, an evolutionary sequence is proposed for the two objects where M1-92 is ~900 yr more evolved than MWC 560.

THE DISCREPANT KINEMATICS OF ORLs AND CELs IN NGC 7009 AS A FUNCTION OF IONIZATION STRUCTURE

We present spatially and velocity-resolved echelle spectroscopy for NGC 7009 obtained with the UVES spectrograph at the European Southern Observatorys Very Large Telescope. Our objective is to analyze the kinematics of emission lines excited by recombination and collisions with electrons to determine whether similarities or differences could be useful in elucidating the well-known abundance discrepancy derived from them. We construct position-velocity maps for recombination, fluorescence, charge transfer, and collisionally excited lines. We find a plasma component emitting in the C II, N II, O II, and Ne II recombination lines whose kinematics are discrepant: they are incompatible with the ionization structure derived from all other evidence and the kinematics derived from all of these lines are unexpectedly very similar. We find direct evidence for a recombination contribution to [N II] λ5755. Once taken into account, the electron temperatures from [N II], [O III], and [Ne III] agree at a given position and velocity. The electron densities derived from [O II] and [Ar IV] are consistent with direct imaging and the distribution of hydrogen emission. The kinematics of the C II, N II, O II, and Ne II lines does not coincide with the kinematics of the [O III] and [Ne III] forbidden emission, indicating that there is an additional plasma component to the recombination emission that arises from a different volume from that giving rise to the forbidden emission from the parent ions within NGC 7009. Thus, the chemical abundances derived from either type of line are correct only for the plasma component from which they arise. Apart from [N II] λ5755, we find no anomaly with the forbidden lines usually used to determine chemical abundances in ionized nebulae, so the abundances derived from them should be reliable for the medium from which they arise.

Iron Depletion in the Hot Bubbles in Planetary Nebulae

We have searched for the emission from [Fe X] λ6374 and [Fe XIV] λ5303 that is expected from the gas emitting in diffuse X-rays in BD +30°3639, NGC 6543, NGC 7009, and NGC 7027. Neither line was detected in any object. Models that fit the X-ray spectra of these objects indicate that the [Fe X] λ6374 emission should be below our detection thresholds, but the predicted [Fe XIV] λ5303 emission exceeds our observed upper limits (1 σ) by factors of at least 3.5-12. The best explanation for the absence of [Fe XIV] λ5303 is that the X-ray plasma is depleted in iron. In principle, this result provides a clear chemical signature that may be used to determine the origin of the X-ray gas in either the nebular gas or the stellar wind. At present, although various lines of evidence appear to favor a nebular origin, the lack of atmospheric and nebular iron abundances in the objects studied here precludes a definitive conclusion.

FITspec: A New Algorithm for the Automated Fit of Synthetic Stellar Spectra for OB Stars

In this paper we describe the FIT\textit{spec} code, a data mining tool for the automatic fitting of synthetic stellar spectra. The program uses a database of 27\,000 {\sc cmfgen} models of stellar atmospheres arranged in a six-dimensional (6D) space, where each dimension corresponds to one model parameter. From these models a library of 2\,835\,000 synthetic spectra were generated covering the ultraviolet, optical, and infrared region of the electromagnetic spectrum. Using FIT\textit{spec} we adjust the effective temperature and the surface gravity. From the 6D array we also get the luminosity, the metallicity, and three parameters for the stellar wind: the terminal velocity (

Database of CMFGEN Models in a 6-Dimensional Space

v_\infty

Integral stellar-nebular model of NGC 7009

), the

M2-9: an attempt to understand its central core

\beta

Stellar Winds of Central Stars of the LMC PNe

exponent of the velocity law, and the clumping filling factor (

The Planetary Nebula M2‐9: Balmer Line Profiles of the Nuclear Region

F_{\rm cl}