arXiv subjects

R. H. Mendez

Publications and source records attributed to R. H. Mendez.

18 recordsLinked to original sources

arXiv2016

The two central stars of NGC 1514: can they actually be related?

The central star of the planetary nebula NGC 1514 is among the visually brightest central stars in the sky (V=9.5). It has long been known to show a composite spectrum, consisting of an A-type star and a much hotter star responsible for the ionization of the surrounding nebula. These two stars have always been assumed to form a binary system. High-resolution spectrograms obtained with Espadons at the CFHT on Mauna Kea have allowed to measure good radial velocities for both stars. They differ by 13 $\pm$ 2 km s$^{-1}$. The stellar velocities have not changed after 500 days. We have also estimated the metallicity of the cooler star. Combining these data with other information available in the literature, we conclude that, unless all the published nebular radial velocities are systematically wrong, the cooler star is just a chance alignment, and the two stars are not orbiting each other. The cooler star cannot have played any role in the formation of NGC 1514.

astro-ph.SR↗

arXiv2011

Planetary nebulae in the elliptical galaxy NGC 4649 (M 60): kinematics and distance redetermination

Using a slitless spectroscopy method with (a) the 8.2 m Subaru telescope and its FOCAS Cassegrain spectrograph, and (b) the ESO Very Large Telescope (VLT) unit 1 (Antu) and its FORS2 Cassegrain spectrograph, we have detected 326 planetary nebulae (PNs) in the giant Virgo elliptical galaxy NGC 4649 (M 60), and we have measured their radial velocities. After rejecting some PNs more likely to belong to the companion galaxy NGC 4647, we have built a catalog with kinematic information for 298 PNs in M 60. Using these radial velocities we have concluded that they support the presence of a dark matter halo around M 60. Based on an isotropic, two-component Hernquist model, we estimate the dark matter halo mass within 3$R_{\rm e}$ to be 4$\times10^{11} M_{\odot}$, which is almost one half of the total mass of about $10^{12} M_{\odot}$ within 3$R_{\rm e}$. This total mass is similar to that estimated from globular cluster, XMM-Newton and Chandra observations. The dark matter becomes dominant outside. More detailed dynamical modeling of the PN data is being published in a companion paper. We have also measured the $m$(5007) magnitudes of many of these PNs, and built a statistically complete sample of 218 PNs. The resulting PN luminosity function (PNLF) was used to estimate a distance modulus of 30.7$\pm$0.2 mag, equivalent to 14$\pm$1 Mpc. This confirms an earlier PNLF distance measurement, based on a much smaller sample. The PNLF distance modulus remains smaller than the surface brightness fluctuation (SBF) distance modulus by 0.4 mag.

astro-ph.GA↗

arXiv2010

Planetary nebulae in the elliptical galaxy NGC 821: kinematics and distance determination

Using a slitless spectroscopy method with the 8.2 m Subaru telescope and its FOCAS Cassegrain spectrograph, we have increased the number of planetary nebula (PN) detections and PN velocity measurements in the flattened elliptical galaxy NGC 821. A comparison with the detections reported previously by the Planetary Nebula Spectrograph (PN.S) group indicates that we have confirmed most of their detections. The velocities measured by the two groups, using different telescopes, spectrographs and slitless techniques, are in good agreement. We have built a combined sample of 167 PNs and have confirmed the keplerian decline of the line-of-sight velocity dispersion reported previously. We also confirm misaligned rotation from the combined sample. A dark matter halo may exist around this galaxy, but it is not needed to keep the PN velocities below the local escape velocity as calculated from the visible mass. We have measured the m(5007) magnitudes of 145 PNs and produced a statistically complete sample of 40 PNs in NGC 821. The resulting PN luminosity function (PNLF) was used to estimate a distance modulus of 31.4 mag, equivalent to 19 Mpc. We also estimated the PN formation rate. NGC 821 becomes the most distant galaxy with a PNLF distance determination. The PNLF distance modulus is smaller than the surface brightness fluctuation (SBF) distance modulus by 0.4 mag. Our kinematic information permits to rule out the idea that a shorter PNLF distance could be produced by the contamination of the PNLF by background galaxies with emission lines redshifted into the on-band filter transmission curve.

astro-ph.CO↗

arXiv2009

Discovery, Photometry, and Kinematics of Planetary Nebulae in M 82

Using an [OIII]5007 on-band/off-band filter technique, we identify 109 planetary nebulae (PNe) candidates in M 82, using the FOCAS instrument at the 8.2m Subaru Telescope. The use of ancillary high-resolution HST ACS H-alpha imaging aided in discriminating PNe from contaminants such as supernova remnants and compact HII regions. Once identified, these PNe reveal a great deal about the host galaxy; our analysis covers kinematics, stellar distribution, and distance determination. Radial velocities were determined for 94 of these PNe using a method of slitless spectroscopy, from which we obtain a clear picture of the galaxy's rotation. Overall, our results agree with those derived by CO(2-1) and HI measurements that show a falling, near-Keplerian rotation curve. However, we find a subset of our PNe that appear to lie far above the plane (~1 kpc), yet these objects appear to be rotating as fast as objects close to the plane. These objects will require further study to determine if they are members of a halo population, or if they can be interpreted as a manifestation of a thickened disk as a consequence of a past interaction with M 81. In addition, [OIII]5007 emission line photometry of the PNe allows the construction of a planetary nebula luminosity function (PNLF). Our PNLF distance determination for M 82 yields a larger distance than those derived using the TRGB, using Cepheid variable stars in nearby group member M 81, or using the PNLF of M 81. We show that this inconsistency most likely stems from our inability to completely correct for internal extinction imparted by this dusty, starburst galaxy. (Abridged)

astro-ph.CO↗

arXiv2008

Kinematics of planetary nebulae in the outskirts of the elliptical galaxy NGC 4697

We describe the implementation of slitless radial velocity measurements of extragalactic planetary nebulae (PNs) with the 8.2 m Subaru telescope and its Cassegrain imaging spectrograph, FOCAS. As a first application, we have extended a previous search for PNs in NGC 4697 to larger angular distances from its center. A total of 218 PNs were detected, and their radial velocities were measured. We have added 56 new PN detections to the existing sample of 535, observed previously with the ESO VLT + FORS imaging spectrograph; 36 of these new 56 PNs are located at angular distances larger than 230 arcsec from the center of NGC 4697. We compare the new FOCAS velocities with the earlier FORS velocities, for 158 of the 162 reobserved sources, finding good agreement. We now have kinematic information extending out to 5 effective radii from the center. The outer line-of-sight velocity dispersion is a bit lower than estimated earlier. This result is compatible with the existence of a dark matter halo plus some degree of radial anisotropy, but the dark matter halo is rather inconspicuous, and it is still unclear how massive it can be. A more detailed global dynamical study of the whole set of PN velocities will be required to decide if they permit to narrow down the range of possible dark matter distributions in NGC 4697. The new radial velocities reveal no evidence of rotation at 5 effective radii.

astro-ph↗

arXiv2008

Toward better simulations of planetary nebulae luminosity functions

We describe a procedure for the numerical simulation of the planetary nebulae luminosity function (PNLF), improving on previous work (Mendez & Soffner 1997). Earlier PNLF simulations were based on an imitation of the observed distribution of the intensities of [O III] 5007 relative to Hbeta, generated predominantly using random numbers. We are now able to replace this by a distribution derived from the predictions of hydrodynamical PN models (Schoenberner et al. 2007), which are made to evolve as the central star moves across the HR diagram, using proper initial and boundary conditions. In this way we move one step closer to a physically consistent procedure for the generation of a PNLF. As an example of these new simulations, we have been able to reproduce the observed PNLF in the Small Magellanic Cloud.

astro-ph↗

arXiv2007

A catalog of planetary nebulae in the elliptical galaxy NGC 4697

We present a catalog of 535 planetary nebulae discovered in the flattened elliptical galaxy NGC 4697, using the FORS1 Cassegrain spectrograph of the Very Large Telescope of the European Southern Observatory at Cerro Paranal, Chile. The catalog provides positions (x, y coordinates relative to the center of light of NGC 4697, as well as RA, Dec.), and, for almost all PNs, the magnitude m(5007) and the heliocentric radial velocity in km/s.

astro-ph↗

arXiv2007

Central stars of planetary nebulae in the Galactic bulge

Optical high-resolution spectra of five central stars of planetary nebulae (CSPN) in the Galactic Bulge have been obtained with Keck/HIRES in order to derive their parameters. Since the distance of the objects is quite well known, such a method has the advantage that stellar luminosities and masses can in principle be determined without relying on theoretical relations between both quantities. By alternatively combining the results of our spectroscopic investigation with evolutionary tracks, we obtain so-called spectroscopic distances, which can be compared with the known (average) distance of the Bulge-CSPN. This offers the possibility to test the validity of model atmospheres and present date post-AGB evolution. We analyze optical H/He profiles of five Galactic Bulge CSPN (plus one comparison object) by means of profile fitting based on state of the art non-LTE modeling tools, to constrain their basic atmospheric parameters (Teff, log g, helium abundance and wind strength). Masses and other stellar radius dependent quantities are obtained from both the known distances and from evolutionary tracks, and the results from both approaches are compared. The major result of the present investigation is that the derived spectroscopic distances depend crucially on the applied reddening law. An "average extinction law" leads to a distance of 10.7 +- 1.2 kpc, which is considerably larger than the Galactic Center distance of 8 kpc. However, we find a remarkable internal agreement of the individual spectroscopic distances of our sample objects. Due to the uncertain reddening correction, the analysis presented here cannot yet be regarded as a consistency check for our method, and a rigorous test of the CSPN evolution theory becomes only possible if this problem has been solved.

astro-ph↗

arXiv2005

Planetary nebulae and stellar kinematics in the flattened elliptical galaxy NGC 1344

We present photometric and kinematic information obtained by measuring 197 planetary nebulae (PNs) discovered in the flattened Fornax elliptical galaxy NGC 1344 (also known as NGC 1340) with an on-band, off-band, grism + on-band filter technique. We build the PN luminosity function (PNLF) and use it to derive a distance modulus m-M=31.4, slightly smaller than, but in good agreement with, the surface brightness fluctuation distance. The PNLF also provides an estimate of the specific PN formation rate: 6x10^-12 PNs per year per solar luminosity. Combining the positional information from the on-band image with PN positions measured on the grism + on-band image, we can measure the radial velocities of 195 PNs, some of them distant more than 3 effective radii from the center of NGC 1344. We complement this data set with stellar kinematics derived from integrated spectra along the major and minor axes, and parallel to the major axis of NGC 1344. The line-of-sight velocity dispersion profile indicates the presence of a dark matter halo around this galaxy.

astro-ph↗

arXiv2005

Oxygen and neon abundances of planetary nebulae in the elliptical galaxy NGC 4697

This paper presents deep spectra of 14 planetary nebulae (PNs) at a variety of angular distances from the center of the flattened elliptical galaxy NGC 4697. Both near the center and among the most outlying PNs we have found several examples of very strong [O III] 5007, about 20 times brighter than Hbeta. This, together with strong [Ne III] lines, implies a lower limit for O and Ne abundances near solar at the center and also at more than two effective radii from the center of NGC 4697. Thus we have found, for the first time from individual stars, direct evidence of the existence of a metal-rich population in elliptical galaxies, confirming metallicities derived from absorption-line indices and extending the information to angular distances where the stellar surface brightness is too low for absorption-line studies. A comparison with abundances obtained closer to the center of NGC 4697 from integrated absorption-line spectra indicates that the metallicity gradient, which is quite steep within one effective radius, becomes much less pronounced beyond one effective radius. The only alternative to this interpretation would be the presence of a very metal-poor PN population with [Z/H] below -1, which we cannot rule out but would require an extremely bimodal metallicity distribution with almost no intermediate metallicities.

astro-ph↗

arXiv2004

Internal kinematics of spiral galaxies in distant clusters. Part II. Observations and data analysis

We have conducted an observing campaign with FORS at the ESO-VLT to explore the kinematical properties of spiral galaxies in distant galaxy clusters. Our main goal is to analyse transformation- and interaction processes of disk galaxies within the special environment of clusters as compared to the hierarchical evolution of galaxies in the field. Spatially resolved MOS-spectra have been obtained for seven galaxy clusters at 0.3 2 hours we reach an S/N>5 in the emission lines appropriate for the deduction of the galaxies' internal rotation velocities from [OII], Hbeta, or [OIII] profiles. Preselection of targets was done on the basis of available redshifts as well as from photometric and morphological information gathered from own observations, archive data, and from the literature. Emphasis was laid on the definition of suitable setups to avoid the typical restrictions of the standard MOS unit for this kind of observations. In total we assembled spectra of 116 objects of which 50 turned out to be cluster members. Position velocity diagrams, finding charts as well as tables with photometric, spectral, and structural parameters of individual galaxies are presented.

astro-ph↗

arXiv2003

Radiation-driven winds of hot luminous stars. XV. Constraints on the mass-luminosity relation of central stars of planetary nebulae

We present a new model atmosphere analysis of nine central stars of planetary nebulae. This study is based on a new generation of realistic stellar model atmospheres for hot stars; state-of-the-art, hydrodynamically consistent, spherically symmetric model atmospheres that have been shown to correctly reproduce the observed UV spectra of massive Population I O-type stars. The information provided by the wind features (terminal velocity, mass loss rate) permits to derive the physical size of each central star, from which we can derive the stellar luminosity, mass and distance, without having to assume a relation between stellar mass and luminosity taken from the theory of stellar structure and AGB and post-AGB evolution. The results of our analysis are quite surprising: we find severe departures from the generally accepted relation between post-AGB central star mass and luminosity.

astro-ph↗

arXiv2001

Intracluster Planetary Nebulae in Virgo: Photometric selection, spectroscopic validation and cluster depth

We have imaged an empty area of 34'x34' one and a half degree north of the Virgo cluster core to survey for intracluster planetary nebula candidates. We have implemented and tested a fully automatic procedure for the selection of emission line objects in wide-field images, based on the on-off technique from Ciardullo and Jacoby. Freeman et al. have spectroscopically confirmed a sample of intracluster planetary nebulae in one Virgo field. We use the photometric and morphological properties of this sample to test our selection procedure. In our newly surveyed Virgo field, 75 objects were identified as best candidates for intracluster PNe. The luminosity function of the spectroscopically confirmed PNe shows a brighter cut-off than the planetary nebula luminosity function for the inner regions of M87. Such a brighter cut-off is also observed in the newly surveyed field and indicates a smaller distance modulus, implying that the front end of the Virgo cluster is closer to us by a significant amount: 14% closer (2.1 Mpc) than M87 for the spectroscopic field, using the PN luminosity function distance of 14.9 Mpc to M87, and 19% closer (2.8 Mpc) than M87 for the newly surveyed field. Independent distance indicators (Tully-Fisher relation for Virgo spirals and surface brightness fluctuations for Virgo ellipticals) agree with these findings. From these two Virgo cluster fields there is no evidence that the surface luminosity density for the diffuse stellar component in the cluster decreases with radius. The luminosity surface density of the diffuse stellar population is comparable to that of the galaxies.

astro-ph↗

arXiv2001

Detection, photometry and slitless radial velocities of 535 planetary nebulae in the flattened elliptical galaxy NGC 4697

We have detected 535 planetary nebulae (PNs) in NGC 4697, using the classic on-band, off-band filter technique with the Focal Reducer and Spectrograph (FORS) at the Cassegrain focus of the first 8-meter telescope unit of the ESO Very Large Telescope. From our photometry we have built the [O III] 5007 planetary nebula luminosity function (PNLF) of NGC 4697. It indicates a distance of 10.5 Mpc, substantially smaller than a previous estimate of 24 Mpc used in earlier dynamical studies. The PNLF also provides an estimate of the specific PN formation rate. Combining the information from on-band images with PN positions on dispersed, slitless grism images, we have obtained radial velocities for 531 of the 535 PNs. They provide kinematic information up to a distance of almost three effective radii from the nucleus. Some rotation is detected in the outer regions, but the rotation curve of this galaxy appears to drop beyond one effective radius. Assuming an isotropic velocity distribution, the velocity dispersion profile is consistent with no dark matter within three effective radii of the nucleus (however, some dark matter can be present if the velocity distribution is anisotropic). We obtain a blue mass-to-light ratio of 11. Earlier M/L ratios for NGC 4697 were too small, because of the too large distance used for their derivation.

astro-ph↗

arXiv2000

Discovery of 9 Ly alpha emitters at redshift z~3.1 using narrow-band imaging and VLT spectroscopy

Narrow-band imaging surveys aimed at detecting the faint emission from the 5007 [O III] line of intracluster planetary nebulae in Virgo also probe high redshift z=3.1 Ly alpha emitters. Here we report on the spectroscopic identification of 9 Ly alpha emitters at z=3.13, obtained with the FORS spectrograph at Unit 1 of the ESO Very Large Telescope (VLT UT1). The spectra of these high redshift objects show a narrow, isolated Ly alpha emission with very faint (frequently undetected) continuum, indicating a large equivalent width. No other features are visible in our spectra. Our Ly alpha emitters are quite similar to those found by Hu (1998), Cowie & Hu (1998) and Hu et al. (1998). Using simple population synthesis models, on the assumption that these sources are regions of star formation, we conclude that the nebulae are nearly optically thick and must have a very low dust content, in order to explain the high observed Ly alpha equivalent widths. For the cosmological and star formation parameters we adopted, the total stellar mass produced would seem to correspond to the formation of rather small galaxies, some of which are perhaps destined to merge. The implied star formation density in our sampled comoving volume is probably somewhat smaller than, but of the same order of magnitude as the star formation density at z=3 derived by other authors from Lyman-break galaxy surveys. This result agrees with the expectation that the Ly alpha emitters are a low-metallicity (or low-dust) tail in a distribution of star forming regions at high redshifts. Finally, the Ly alpha emitters may contribute as many H-ionizing photons as QSOs at z=3.

astro-ph↗

arXiv1999

Intracluster Planetary Nebulae in the Virgo Cluster

We briefly describe the properties of the confirmed spectroscopic sample of intracluster planetary nebulae recently discovered in the Virgo cluster. We find 23 bonafide intracluster planetary nebulae and 8 high redshift (z ~ 3.1) Lyalpha emitters identified by their broad asymmetric emission line.

astro-ph↗

arXiv1998

The stellar dynamics and mass of NGC 1316 using the radial velocities of planetary nebulae

We present a study of the kinematics of the outer regions of the early-type galaxy NGC 1316, based on radial velocity measurements of 43 planetary nebulae as well as deep integrated-light absorption line spectra. The smoothed velocity field of NGC 1316 indicates fast rotation at a distance of 16 kpc, possibly associated with an elongated feature orthogonal to the inner dust lanes. The mean square stellar velocity is approximately independent of radius, and the estimated total mass of the system is 2.6 x 10^11 M_sun within a radius of 16 kpc, implying an integrated mass-to-light ratio of M/L_B = 8.

astro-ph↗

arXiv1997

More evidence for an intracluster planetary nebulae population in the Virgo cluster

We surveyed a 50 sq arcmin region in the Virgo cluster core to search for intergalactic planetary nebulae, and found 11 candidates in the surveyed area. The measured fluxes of these unresolved sources are consistent with these objects being planetary nebulae from an intracluster population of stars. We compute the cumulative luminosity function of these 11 planetary nebula candidates. If we assume that they belong to the Virgo cluster, their cumulative luminosity function is in good agreement with planetary nebula luminosity function simulations. This comparison allows us to estimate the surface mass density of the intracluster stellar population at the surveyed field in the cluster core.

astro-ph↗