arXiv subjects

George H. Jacoby

Publications and source records attributed to George H. Jacoby.

At least 37 records · Page 2Linked to original sources

arXiv2010

Planetary Nebulae towards the Galactic bulge. I. [OIII] fluxes

We present [OIII]λ5007 fluxes and angular diameters for 435 Planetary Nebulae (PN) in the central 10' x 10' region towards the Galactic bulge. Our sample is taken from the new discoveries of the MASH PN surveys as well as previously known PN. This sample accounts for 80% of known PN in this region. Fluxes and diameters are measured from narrow-band imaging with the MOSAIC-II camera on the 4-m Blanco telescope at the Cerro-Tololo Inter-American Observatory. This is the largest (~60 square degrees), uniform [OIII]λ5007 survey of the inner Galactic bulge ever undertaken. 104 of the objects have measured [OIII]λ5007, [OIII]λ4959, Hα or Hβ fluxes from the literature, which we use to undertake a detailed comparison to demonstrate the integrity of our new fluxes. Our independent measurements are in excellent agreement with the very best literature sources over two orders of magnitude, while maintaining good consistency over five orders of magnitude. The excellent resolution and sensitivity of our data allows not only for a robust set of homogenous PN fluxes, but provides greater detail into their intricate, otherwise undetermined [OIII]λ5007 morphologies. These new, extensive measurements significantly increase the sample of reliable [OIII]λ5007 fluxes for Galactic bulge PN making it a valuable resource and a prelude to the construction of our new Galactic bulge Planetary Nebula luminosity function (Paper II).

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arXiv2010

A Survey of Local Group Galaxies Currently Forming Stars: II. UBVRI Photometry of Stars in Seven Dwarfs and a Comparison of the Entire Sample

We have obtained UBVRI images with the Kitt Peak and Cerro Tololo 4-m telescopes and Mosaic cameras of seven dwarfs in (or near) the Local Group, all of which have known evidence of recent star formation: IC10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus,and Phoenix. We construct color-magnitude diagrams (CMDs) of these systems, as well as neighboring regions that can be used to evaluate the degree of foreground contamination by stars in the Milky Way. Inter-comparison of these CMDs with those of M31, M33, the LMC, and the SMC permits us to determine improved reddening values for a typical OB star found within these galaxies. All of the CMDs reveal a strong or modest number of blue supergiants. All but Pegasus and Phoenix also show the clear presence of red supergiants in the CMD, although IC10 appears to be deficient in these objects given its large WR population. The bright stars of intermediate color in the CMD are badly contaminated by foreground stars (30-100%), and considerable spectroscopy is needed before statistics on the yellow supergiants in these systems will be known. This study is intended to serve both as the impetus and "finding charts" for further space-based imaging, and for many spectroscopic programs at large aperture.

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arXiv2009

Searching for Faint Planetary Nebulae Using the Digital Sky Survey

Recent Halpha surveys such as SHS and IPHAS have improved the completeness of the Galactic planetary nebula (PN) census. We now know of ~3,000 PNe in the Galaxy, but this is far short of most estimates, typically ~25,000 or more for the total population. The size of the Galactic PN population is required to derive an accurate estimate of the chemical enrichment rates of nitrogen, carbon, and helium. In addition, a high PN count (~20,000) is strong evidence that most 1-8 Msun main sequence stars will go through a PN phase, while a low count (<10,000) argues that special conditions (e.g., a close binary interaction) are required to form a PN. We describe a technique for finding hundreds more PNe using the existing data collections of the digital sky surveys, thereby improving the census of Galactic PNe.

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arXiv2009

The edge of the M87 halo and the kinematics of the diffuse light in the Virgo cluster core

We present high resolution FLAMES/VLT spectroscopy of intracluster planetary nebula (ICPN) candidates, targeting three new fields in the Virgo cluster core with surface brightness down to mu_B = 28.5. Based on the projected phase space information we separate the old and 12 newly-confirmed PNs into galaxy and intracluster components. The M87 PNs are confined to the extended stellar envelope of M87, within a projected radius of ~ 160 kpc, while the ICPNs are scattered across the whole surveyed region between M87 and M86. The velocity dispersions determined from the M87 PNs at projected radii of 60 kpc and 144 kpc show that the galaxy's velocity dispersion profile decreases in the outer halo, down to 78 +/- 25 km/s. A Jeans model for the M87 halo stars in the gravitational potential traced by the X-ray emission fits the observed velocity dispersion profile only if the stellar orbits are strongly radially anisotropic (beta ~= 0.4 at r ~= 10 kpc increasing to 0.8 at the outer edge), and if additionally the stellar halo is truncated at ~= 150 kpc average elliptical radius. From the spatial and velocity distribution of the ICPNs we infer that M87 and M86 are falling towards each other and that we may be observing them just before the first close pass. The inferred luminosity-specific PN numbers for the M87 halo and the ICL are in the range of values observed for old (> 10 Gyr) stellar populations (abridged).

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arXiv2008

Expansion velocities and core masses of bright planetary nebulae in the Virgo cluster

The line-of-sight velocities and [OIII] 5007 AA expansion velocities are measured for 11 planetary nebulae (PNs) in the Virgo cluster core, at 15 Mpc distance, with the FLAMES spectrograph on the ESO VLT. These PNs are located about halfway between the two giant ellipticals M87 and M86. From the [OIII] 5007 AA line profile widths, the average half-width at half maximum expansion velocity for this sample of 11 PNs is v_HWHM = 16.5 km/s (RMS=2.6 km/s). We use the PN subsample bound to M87 to remove the distance uncertainties, and the resulting [OIII] 5007 AA luminosities to derive the central star masses. We find these masses to be at least 0.6 M_sun and obtain PN observable life times t_PN < 2000 yrs, which imply that the bright PNs detected in the Virgo cluster core are compact, high density nebulae. We finally discuss several scenarios for explaining the high central star masses in these bright M87 halo PNs.

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arXiv2007

A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars

We describe a search for H-alpha emission-lined stars in M31, M33, and seven dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus and the Phoenix dwarf) using interference filter imaging with the KPNO and CTIO 4-m telescope and Mosaic cameras. The survey is aimed primarily at identifying new Luminous Blue Variables (LBVs) from their spectroscopic similarity to known LBVs, avoiding the bias towards photometric variability, which may require centuries to manifest itself if LBVs go through long quiescent periods. Followup spectroscopy with WIYN confirms that our survey detected a wealth of stars whose spectra are similar to the known LBVs. We "classify" the spectra of known LBVs, and compare these to the spectra of the new LBV candidates. We demonstrate spectacular spectral variability for several of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet star, which now shows FeI, FeII and Balmer emission lines but neither the NIII 4634,42 nor HeII 4686 emission that it did in 1982. Profound spectral changes are also noted for other suspected and known LBVs. Several of the LBV candidates also show >0.5 mag changes in V over the past 10-20 years. The number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822, and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be several hundred, in contrast to the 8 known historically through large-scale photometric variability. This has significant implications for the time scale of the LBV phase. We also identify a few new WRs and peculiar emission-lined objects.

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arXiv2006

Calibrating Type Ia Supernovae using the Planetary Nebula Luminosity Function I. Initial Results

We report the results of an [O III] lambda 5007 survey for planetary nebulae (PN) in five galaxies that were hosts of well-observed Type Ia supernovae: NGC 524, NGC 1316, NGC 1380, NGC 1448 and NGC 4526. The goals of this survey are to better quantify the zero-point of the maximum magnitude versus decline rate relation for supernovae Type Ia and to validate the insensitivity of Type Ia luminosity to parent stellar population using the host galaxy Hubble type as a surrogate. We detected a total of 45 planetary nebulae candidates in NGC 1316, 44 candidates in NGC 1380, and 94 candidates in NGC 4526. From these data, and the empirical planetary nebula luminosity function (PNLF), we derive distances of 17.9 +0.8/-0.9 Mpc, 16.1 +0.8/-1.1 Mpc, and 13.6 +1.3/-1.2 Mpc respectively. Our derived distance to NGC 4526 has a lower precision due to the likely presence of Virgo intracluster planetary nebulae in the foreground of this galaxy. In NGC 524 and NGC 1448 we detected no planetary nebulae candidates down to the limiting magnitudes of our observations. We present a formalism for setting realistic distance limits in these two cases, and derive robust lower limits of 20.9 Mpc and 15.8 Mpc, respectively. After combining these results with other distances from the PNLF, Cepheid, and Surface Brightness Fluctuations distance indicators, we calibrate the optical and near-infrared relations for supernovae Type Ia and we find that the Hubble constants derived from each of the three methods are broadly consistent, implying that the properties of supernovae Type Ia do not vary drastically as a function of stellar population. We determine a preliminary Hubble constant of H_0 = 77 +/- 3 (random) +/- 5 (systematic) km/s/Mpc for the PNLF, though more nearby galaxies with high-quality observations are clearly needed.

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arXiv2006

The Resolved Stellar Populations of a Dwarf Spheroidal Galaxy in the Virgo Cluster

We report on the discovery of a faint (M_V ~ -10.6 +/- 0.2) dwarf spheroidal galaxy on deep F606W and F814W Hubble Space Telescope images of a Virgo intracluster field. The galaxy is easily resolved in our images, as our color magnitude diagram (CMD) extends > 1 magnitude beyond the tip of the red giant branch (RGB). Thus, it is the deepest CMD for a small dwarf galaxy inside a cluster environment. Using the colors of the RGB stars, we derive a metal abundance for the dwarf of [M/H]= -2.3 +/- 0.3, and show that the metallicity dispersion is less than 0.6 dex at 95% confidence. We also use the galaxy's lack of AGB stars and the absence of objects brighter than M_bol ~ -4.1 +/- 0.2 to show that the system is old (t >~10 Gyr). Finally, we derive the object's structural parameters, and show that the galaxy displays no obvious evidence of tidal threshing. Since the tip of the red giant branch distance ((m-M)_0 = 31.23 +/- 0.17 or D = 17.6 +/- 1.4 Mpc) puts the galaxy near the core of the Virgo cluster, one might expect the object to have undergone some tidal processing. Yet the chemical and morphological similarity between the dwarf and the dSph galaxies of the Local and M81 Group demonstrates that the object is indeed pristine, and not the shredded remains of a much larger galaxy. We discuss the possible origins of this galaxy, and suggest that it is just now falling into Virgo for the first time.

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arXiv2006

The Metallicity Distribution of Intracluster Stars in Virgo

We have used the Hubble Space Telescope's Advanced Camera for Surveys (ACS) to detect and measure ~5300 stars in a single intracluster field in the Virgo Cluster. By performing F606W and F814W photometry on these stars, we have determined their metallicity distribution function, and constrained the types of stars present in this portion of Virgo's intracluster space. Based on the small number of stars detected brighter than the red giant branch (RGB) tip, we suggest that in this region, Virgo's intracluster stars are mostly old (>~10 Gyr). Through analysis of the RGB stars themselves, we determine that the population contains the full range of metallicities probed (-2.3<[M/H]<0.0). We also present evidence that the younger (<10 Gyr) component of the population is more metal-rich, with [M/H]>-0.5. The spatial distribution of the most metal-poor stars in the field shows significantly more structure than that of the metal-rich stars, indicating that the intracluster population is not well-mixed. We discuss the implications these observations have for the production of intracluster stars and the dynamical evolution of the Virgo Cluster.

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arXiv2006

Virgo's Intracluster Globular Clusters as Seen by the Advanced Camera for Surveys

We report the discovery of 4 candidate intracluster globular clusters (IGCs) in a single deep HST ACS field of the Virgo Cluster. We show that each cluster is roughly spherical, has a magnitude near the peak of the Virgo globular cluster luminosity function, has a radial profile that is best-fit by a King model, and is surrounded by an excess of point sources which have the colors and magnitudes of cluster red giant stars. Despite the fact that two of our IGC candidates have integrated colors redder than the mean of the M87 globular cluster system, we propose that all of the objects are metal-poor with [M/H] < -1. We show that the tidal radii of our intracluster globulars are all larger than the mean for Milky Way clusters, and suggest that the clusters have undergone less tidal stress than their Galactic counterparts. Finally, we normalize our globular cluster observations to the luminosity of intracluster stars, and derive a value of S_N ~ 6 for the specific frequency of Virgo intracluster globular clusters. We use these data to constrain the origins of Virgo's intracluster population, and suggest that globular clusters in our intracluster field have a different origin than globular clusters in the vicinity of M87. In particular, we argue that dwarf elliptical galaxies may be an important source of intracluster stars.

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arXiv2006

A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33

We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq degrees of M33, chosen so as to include all of the regions currently active in forming massive stars. The catalog contains 371,781 and 146,622 stars in M31 and M33, respectively, where every star has a counterpart (at least) in B, V, and R. We compare our photometry to previous studies. We provide cross references to the stars confirmed as members by spectroscopy, and compare the location of these to the complete set in color-magnitude diagrams. While follow-up spectroscopy is needed for many projects, we demonstrate the success of our photometry in being able to distinguish M31/M33 members from foreground Galactic stars. We also present the results of newly obtained spectroscopy, which identifies 34 newly confirmed members, including B-A supergiants, the earliest O star known in M31, and two new Luminous Blue Variable candidates whose spectra are similar to that of P Cygni.

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arXiv2005

Close Binaries as the Progenitors of the Brightest Planetary Nebulae

We investigate the possible progenitors of the planetary nebulae (PNs) which populate the top 0.5 mag of the [O III] 5007 planetary nebula luminosity function (PNLF). We show that the absolute luminosity of the PNLF cutoff demands that the central stars of these most luminous planetaries be greater than 0.6 Msun, and that such high-mass PN cores must exist in every galaxy. We also use the bolometric-luminosity specific PN number density to show that in early-type galaxies, [O III]-bright planetaries are relatively rare, with only about 10% of stars evolving to these bright magnitudes. We demonstrate that the combination of these two facts implies that either all early-type systems contain a small, smoothly distributed component of young (< 1 Gyr old) stars, or another mechanism exists for creating high-core mass planetaries. We argue that binary-star evolution is this second mechanism, and demonstrate that blue stragglers have the appropriate core properties and number density to explain the observations. We discuss the implications of this alternative mode of stellar evolution, and speculate on how coalesced binaries might affect the use of PNs for measuring a galaxy's star-formation history and chemical evolution.

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arXiv2005

The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda I and Andromeda III

(Abridged) We present the results of variable star searches of the M31 dwarf spheroidal companions Andromeda I and Andromeda III using the Hubble Space Telescope. A total of 100 variable stars were found in Andromeda I, while 56 were found in Andromeda III. One variable found in Andromeda I and another in Andromeda III may be Population II Cepheids. In addition to this variable in Andromeda III, another four variables are anomalous Cepheids. We found 72 fundamental mode RR Lyrae stars and 26 first-overtone mode RR Lyrae stars in Andromdea I giving mean periods of 0.575 day and 0.388 day, respectively. One likely RR Lyrae was not classified. For Andromeda III, 39 RR Lyrae stars are pulsating in the fundamental mode with a mean period of 0.657 day and 12 are in the first-overtone mode with a mean period of 0.402 day. While Andromeda I has a mean period that is consistent with its metallicity, the mean period of the fundamental mode RR Lyrae in Andromeda III is larger than expected. In Andromeda I, we found two RR Lyrae stars which are noticeably fainter than the horizontal branch. We discuss the possibility that these stars are associated with the recently discovered stellar stream in the halo of M31. We find =25.14+/-0.04 mag for Andromeda I resulting in a distance of 765+/-25 kpc. For Andromeda III, =25.01+/-0.04 mag giving a distance of 740+/-20 kpc. The relation between specific frequency of anomalous Cepheids and mean metallicity of the galaxy in the M31 dwarf spheroidal galaxies follows the same relation as the Galactic dwarf spheroidal galaxies.

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arXiv2004

The Planetary Nebula System of M33

We report the results of a photometric and spectroscopic survey for planetary nebulae (PNe) in the Local Group spiral galaxy M33. We use our sample of 152 PNe to derive an [O III] planetary nebula luminosity function (PNLF) distance of (m-M)_0 = 24.86^+0.07-0.11 (0.94^+0.03-0.05 Mpc). Although this value is ~ 15% larger than the galaxy's Cepheid distance, the discrepancy likely arises from differing assumptions about the system's internal extinction. Our photometry (which extends >3 mag down the PNLF), also reveals that the faint-end of M33's PN luminosity function is non-monotonic, with an inflection point ~2 mag below the PNLF cutoff. We argue that this feature is due to the galaxy's large population of high core-mass planetaries, and that its amplitude may eventually be useful as a diagnostic for studies of stellar populations. Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33's PN population rotates along with the old disk, with a small asymmetric drift of \~ 10km/s. Remarkably, the population's line-of-sight velocity dispersion varies little over ~4 optical disk scale lengths, with sigma_{rad}~20km/s. We show that this is due to a combination of factors, including a decline in the radial component of the velocity ellipsoid at small galactocentric radii, and a gradient in the ratio of the vertical to radial velocity dispersion. We use our data to show that the mass scale length of M33's disk is ~2.3 times larger than that of the system's IR luminosity and that the disk's V-band mass-to-light ratio changes from M/L_V ~0.3 in the galaxy's inner regions to M/L_V ~2.0 at ~9 kpc. Models in which the dark matter is distributed in the plane of the galaxy are excluded by our data. (abridged)

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arXiv2004

Planetary Nebulae Near the Galactic Center: Identifications

We surveyed the central 4 x 4 degrees of the Galactic center for planetary nebulae in the light of [S III] 9532 A and found 94 PNe that were not previously known, plus 3 that were previously identified as possible candidates. For 63 of these 97 objects, we obtained spectra that are consistent with highly reddened PN while the other 34 could not be recovered spectroscopically and remain unverified. Of the 94 candidates, 54 and 57 were detected via radio at 3 and 6 cm, respectively. An additional 20 PNe candidates were found during follow-up Halpha imaging but have not yet been verified spectroscopically. Based on the properties of IRAS sources in this region of the Galaxy, and on the total luminosity of the Galactic bulge, the expected number of PNe is ~250, only 50 % more than the 160 PNe candidates now known. Thus, surveys for PNe in the bulge are approximately two-thirds complete with the remainder likely hidden behind dust.

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arXiv2003

Intracluster Planetary Nebulae in Clusters and Groups

We present the results from multiple surveys for intracluster planetary nebulae (IPNe) in nearby galaxy clusters and groups. We find that in the case of clusters, our observations imply: 1) the amount of intracluster starlight is significant, up to 20% of the total starlight, 2) the Virgo Cluster is elongated along our line of sight, and 3) the intracluster light is clustered on the sky, implying ongoing tidal stripping. In contrast, searches for IPNe in groups have found little or no intra-group population, implying there may be something in the cluster environment that significantly enhances intracluster star production. From high-resolution N-body simulations, we find that the IPNe should create observable features in position-velocity space, and that these features may eventually allow us to place limits on the dynamics of galaxy clusters.

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arXiv2003

The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda II

(abridged) We present the results of a variable star search in Andromeda II, a dwarf spheroidal galaxy companion to M31, using HST/WFPC2 observations. Seventy-three variables were found, one of which is an anomalous Cepheid while the others are RR Lyrae stars. The anomalous Cepheid has properties consistent with those found in other dwarf spheroidal galaxies. For the RR Lyrae stars, the mean periods are 0.571 day and 0.363 day for the fundamental mode and first-overtone mode stars, respectively. With this fundamental mode mean period and the mean metallicity determined from the red giant branch (<[Fe/H]>=-1.49), Andromeda II follows the period-metallicity relation defined by the Galactic globular clusters and other dwarf spheroidal galaxies. We also find that the properties of the RR Lyrae stars themselves indicate a mean abundance that is consistent with that determined from the red giants. There is, however, a significant spread among the RR Lyrae stars in the period-amplitude diagram, which is possibly related to the metallicity spread in Andromeda II indicated by the width of the red giant branch in Da Costa et al. In addition, the abundance distribution of the RR Lyrae stars is notably wider than the distribution expected from the abundance determination errors alone. The mean magnitude of the RR Lyrae stars, =24.87+/-0.03, implies a distance d=665+/-20 kpc to Andromeda II. We also demonstrate that the specific frequency of anomalous Cepheids in dwarf spheroidal galaxies correlates with the mean metallicity of their parent galaxy, and that the Andromeda II and Andromeda VI anomalous Cepheids appear to follow the same relation as those in the Galactic dwarf spheroidals.

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arXiv2002

Kinematics of Planetary Nebulae in M51's Tidal Debris

We report the results of a radial velocity survey of planetary nebulae (PNe) located in the tidal features of the well-known interacting system NGC 5194/95 (M51). We find clear kinematic evidence that M51's northwestern tidal debris consists of two discrete structures which overlap in projection -- NGC 5195's own tidal tail, and diffuse material stripped from NGC 5194. We compare these kinematic data to a new numerical simulation of the M51 system, and show that the data are consistent with the classic ``single passage'' model for the encounter, with a parabolic satellite trajectory and a 2:1 mass ratio. We also comment on the spectra of two unusual objects: a high-velocity PN which may be associated with NGC 5194's halo, and a possible interloping high-redshift galaxy.

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