K-band Magnitudes Research Articles

A theoretical analysis of the systematic errors in the red clump distance to the Large Magellanic Cloud (LMC)

We present a detailed analysis of the uncertainty on the theoretical population corrections to the Large Magellanic Cloud (LMC) red clump (RC) absolute magnitude, by employing a population synthesis algorithm to simulatetheoretically the photometric and spectroscopic properties of RC stars, under various assumptions concerning the LMC star formation rate (SFR) and age-metallicity relationship (AMR). A comparison of the outcome of our simulations with observations of evolved low- to intermediate-mass stars in the LMC allows one to select the combinations of SFR and AMR that bracket the real LMC star formation history, and to estimate the systematic error on the associated RC population corrections. The most accurate estimate of the LMC distance modulus from the RC method (adopting the OGLE-II reddening maps for the LMC) is obtained from the K-band magnitude, and provides (m - M) 0 , L M C = 18.47 ′ 0.01(random) + 0 . 0 5 -0.06(systematic). Distances obtained from the I band, or from the multicolour RC technique which determines at the same time reddening and distance, both agree (albeit with a slightly larger error bar) with this value.

The RR Lyrae star period –K-band luminosity relation of the globular cluster M 3

That the RR Lyrae star period - K-band luminosity relation is a promising tool as a distance indicator in the Milky Way and Local Group of galaxies is apparent on observational and theoretical grounds in the literature. Less clear is the sensitivity of the relation, and consequently the physics of horizontal branch stars, to differences in stellar environment. In this paper, the first measurement of the (fundamental) period - K-band luminosity relation for the central region of a globular cluster is presented. It is based on a sample of seven RR Lyrae stars imaged with adaptive optics. In addition, the relation for the outer region has been reanalyzed, and is found to be in good agreement with both the previous estimate by Longmore et al. (1990), and with the inner region relation, especially when irregular and double-mode RR Lyrae stars are excluded. Importantly, there is no difference between the slope of the inner and outer region relation within measurement uncertainties, suggesting no difference in evolutionary state (luminosity). Taking the M 3 distance modulus as 15.0 ′ 0.07 mag, the period-absolute K-band magnitude relation derived by linear least squares fitting is: M K = -0.96 (′0.10) - 2.42 (′0.16) Log P o for the inner region. Excluding irregular variable stars, the outer region relation is: M K = -1.07 (′0.10) - 2.38 (′0.15) Log P o . This good agreement provides further strong support for the near-IR period-luminosity relation as a distance indicator.

Near-infrared imaging of ellipticals: surface brightness profiles and photometry

We present near-infrared K-band imaging of a large sample of candidate merger remnant galaxies and Hickson Compact Group ellipticals. We derive light profile indices, effective radii and surface brightnesses, as well as total K-band magnitudes. We find that the light distributions of the merger remnant candidates are consistent with those of ‘normal’ ellipticals, and scatter around a mean profile index of (1/n) = 0.20. Many of our sample galaxies have surface brightness profiles that are not well described by a de Vaucouleurs law (1/n = 0.25), and we discuss the implications of this on the derived total magnitudes. Comparing the total K magnitudes calculated by extrapolating a de Vaucouleurs profile and those derived using a generalized S´

The Araucaria Project: Dependence of MeanK,J, andIAbsolute Magnitudes of Red Clump Stars on Metallicity and Age

As a part of our ongoing Araucaria Project on the improvement of stellar distance indicators we present deep near-infrared JK imaging of several fields in four Local Group galaxies: LMC, SMC, and the Carina and Fornax dwarf galaxies. These data were obtained under excellent seeing conditions at the European Southern Observatory Very Large Telescope and New Technology Telescope. We determine the mean red clump star magnitudes in the J and K bands in the four galaxies. A comparison of the extinction-corrected K-band red clump star magnitudes with the tip of the red giant branch magnitude, the mean RR Lyrae star V-band magnitude, and the mean K-band magnitude of Cepheid variables at a period of 10 days (for the LMC and SMC) strongly suggests that the red clump star absolute K-band magnitude has a very low (if any) dependence on metallicity over the broad range of metallicities covered by our target galaxies. This finding is in contrast to the mean I- and J-band red clump star magnitudes, which do have a clear metallicity dependence and which we calibrate from our data. Excellent agreement with the former calibration of the red clump I-band magnitude dependence on metallicity of Udalski is found from our new data. We use the Galactic cluster K-band red clump star data of Grocholski & Sarajedini to demonstrate that the K-band red clump star absolute magnitude also has very little (if any) dependence on age over an age range of about 2–8 Gyr. The present study therefore provides clear evidence that the mean K-band magnitude of red clump stars is an excellent distance indicator, with very small (if any) population corrections to be applied over a large range in metallicity and age. Our findings imply that present-day population corrections calculated from models are only accurate at a ±0.15 mag level, which is a great achievement in itself but not accurate enough for high-precision distance scale work. We determine the distances to all our target galaxies from the K-band red clump magnitude, with very small statistical uncertainties. Comparing these distances with those coming from the observed mean I-band magnitudes of the red clump stars, we find evidence that there is likely to be a problem in the photometric calibration of the local, solar neighborhood red clump star K- or I-band magnitudes, which amounts to some 0.2 mag. A redetermination of the absolute photometric calibration of the Hipparcos-observed nearby red clump stars seems necessary to resolve this problem and put the derivation of absolute distances to Local Group galaxies from their red clump stars on a firmer basis.

A Search for Close Binaries in the ρ Ophiuchi Star‐forming Region

We have carried out a new, near-infrared speckle imaging survey of 19 members of the young stellar popu- lation in the nearby (d ¼ 140 pc) � Oph cloud core. Results for four binary and one newly discovered triple system are reported. Data for all known multiple systems among the pre-main-sequence population ofOph are tabulated. We define a restricted binary fraction, Fb;r, and a restricted companion fraction, Fc;r, as counting only those systems most detectable in the present and previous high-resolution near-infrared imaging surveys having separations between 0> 1a nd� 1>1 and K-band magnitude differences DK < 3. Analysis of all the available multiplicity data results in updated values of Fb;r ¼ 24% � 11% and Fc;r ¼ 24% � 11% for the Ophiuchus pre-main-sequence population. These values are consistent with the values in the Taurus star- forming region, and Fc;r is in excess by a factor of 2 relative to the main sequence at the 1 � level. Subject headings: binaries: close — infrared: stars — stars: pre-main-sequence — techniques: high angular resolution

Deep Near-Infrared Observations and Identifications of [ITAL]Chandra[/ITAL] Sources in Orion Molecular Clouds 2 and 3

We conducted deep near-infrared (NIR) imaging observations of Orion molecular clouds 2 and 3 using the Quick Infrared Camera on the 88 inch (2.2 m) telescope of the University of Hawaii. Our purposes were (1) to generate a comprehensive NIR source catalog of these star-forming clouds and (2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the Two Micron All Sky Survey (2MASS) catalog. Our J-, H-, and K-band observations are ~2 mag deeper than those of 2MASS and match the current Chandra observation well. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for ~42% of the 2MASS unidentified Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.

An Obscured Radio Galaxy at High Redshift

Perhaps as many as 10% of high-redshift radio galaxy (z > 2) candidates that are selected using an ultrasteep radio spectrum criterion fail to show optical emission (continuum, lines) in deep Keck exposures. Their parent objects are only detected in the near-IR and are probably heavily obscured and/or at very high redshift. To search for signatures of dust and help constrain the nature and redshifts of these no-z radio galaxies, we have conducted a program of submillimeter and millimeter observations. Here we report the first results of a detailed study of one of these objects, WN J0305+3525. It appears associated with a small group of K ~ 21-22 objects and is strongly detected at both 850 μm and 1.25 mm. On the basis of its faint K-band magnitude, spectral energy distribution, and other evidence, we estimate that the radio galaxy is probably at a redshift z 3 ± 1. This would make WN J0305+3525 a radio-loud hyperluminous infrared galaxy (LFIR ~ 1013 L☉) similar to, but more obscured than, other dusty radio galaxies in this redshift range. This, together with the absence of Lyα emission and compact (θ 19) radio structure, suggests that WN J0305+3525 is embedded in a very dense, dusty medium and is probably at an early stage of its formation.

The log P - $\langle M_{K}\rangle$ Relation of Galactic Field RR Lyrae Variables

The kinematical parameters of the local field RR Lyrae population and the zero-point of the log relation for these variables are inferred by applying the statistical parallax (maximum-likeli-hood) technique to a sample of 182 RR Lyraes with known periods, radial-velocities, metallicities, K-band photometry, and absolute proper motions on the ICRS system. Hipparcos, Tycho-2, SPM, UCAC, NPM1, and the Four-Million Star Catalog (Volchkov et al. 1992) were used as the sources of proper motions; the proper motions of the last two catalogs are reduced to the Hipparcos (ICRS) system (Dambis & Rastorguev 2001). The K-band magnitudes were adopted from the list of Fernley et al. (1998) and supplemented by the data of the 2MASS Second Incremental Data Release. The parameters of the velocity distribution are found to be: (, , km s-1; (, , ) km s-1: and (, , ) km s-1; (, , ) km s-1 for the thick-disk (41 stars) and halo (141 stars) objects, respectively. The zero-point of the infrared PL relation of Jones et al. (1992) (based on the results obtained using the Baade-Wesselink method) is confirmed: we find compared to as inferred by Jones et al. (1992). A conversion of the resulting log relation to V-band luminosities yields the metallicity-luminosity relation Fe/H. Our results imply a solar Galactocentric distance of kpc and an LMC distance modulus of (cluster RR Lyraes) or (field RR Lyraes), thereby favoring the so-called short distance scale.

Near-infrared imaging and the K--z relation for radio galaxies in the 7C Redshift Survey

We present K-band imaging of all 49 radio galaxies in the 7C-I and 7C-II regions of the 7C Redshift Survey (7CRS). The low-frequency (151-MHz) selected 7CRS sample contains all sources with flux densities S 1 5 1 > 0.5 Jyin three regions of the sky. We combine the K-band magnitudes of the 7CRS radio galaxies with those from the 3CRR, 6CE and 6C* samples to investigate the nature of the relationship between K-magnitude and redshift and whether there is any dependence upon radio luminosity. We find that radio galaxies appear to belong to a homogeneous population that formed the bulk of their stars at high redshifts (z f > 5) and evolved passively from then until they reach a mean present-day luminosity of 3 L * . We find a significant difference between the K-magnitudes of the 7CRS and 3CRR radio galaxies with the 7CRS galaxies being 0.55 mag fainter at all redshifts. The cause of this weak correlation between stellar and radio luminosities probably lies in mutual correlations of these properties with the central black hole mass. We compare the evolution-corrected host luminosities at a constant radio luminosity and find that the typical host luminosity (mass) increases by approximately 1 L * from z ∼ 2 to ∼0.5 which, although a much smaller factor than predicted by semi-analytic models of galaxy formation, is in line with results on optically selected quasars. Our study has therefore revealed that the small dispersion in stellar luminosity of radio galaxies around 3 L * includes subtle but significant differences between the host galaxies of extreme- and moderate-power radio sources at fixed redshift, and between hose of high- and low-redshift radio sources at fixed radio luminosity.

Optical and Near-Infrared Imaging of Ultra–Steep-Spectrum Radio Sources: The [ITAL]K[/ITAL]-[CLC][ITAL]z[/ITAL][/CLC] Diagram of Radio-selected and Optically Selected Galaxies

We present optical and/or near-IR images of 128 ultra?steep-spectrum radio sources. Roughly half of the objects are identified in the optical images (R 24), while in the near-IR images, more than 94% are detected at K 22. The mean K magnitude is = 19.26 within a 2'' diameter aperture. The distribution of R-K colors indicates that at least one-third of the objects observed have very red colors (R-K > 5). The major axes of the identifications in the K band are preferentially oriented along the radio axes, with half of them having compact morphologies. The 22 sources with spectroscopic redshifts and K-band magnitudes follow the K-z relation found from previous radio samples, but with a larger scatter. We argue that this may be due to a dependence of K magnitude on the radio power, with the most luminous radio sources inhabiting the most massive host galaxies. We present a composite K-z diagram of radio-loud and radio-quiet galaxies, selected from the Hubble Deep Field (North) and the Hawaii surveys. Out to z 1, the radio-loud galaxies trace the bright envelope of the radio quiet galaxies, while at z 1, the radio-loud galaxies are 2 mag brighter. We argue that this is not due to a contribution from the active galactic nucleus or emission lines. This difference strongly suggests that radio galaxies pinpoint the most massive systems out to the highest known redshifts, probably as a result of the mutual correlation of the mass of the galaxy and the radio power on the mass of the central black hole.

A Mid-Infrared Study of the Young Stellar Population in the NGC 2024 Cluster

We present the results of the first broadband 10.8 um survey of the NGC 2024 cluster. The mid-infrared data were combined with our previously published JHKL photometry in order to construct spectral energy distributions for all detected sources. The main scientific goals were to investigate the nature of the young stellar objects (YSOs) in the cluster, and to examine the efficiency of detecting circumstellar disk sources from near-infrared JHKL color-color diagrams. Out of 59 sources surveyed having K-band magnitudes K < 10.5, we detected 35 (~59%) at 10 um. Combining these detections, and upper limits for the non-detections, with existing JHKL data, we identify 1 Class I, 6 flat spectrum, 28 Class II and 5 Class III sources. We find a circumstellar disk fraction for NGC 2024 of ~85% +/- 15%, which confirms earlier published suggestions that the majority, if not all, of the stars in NGC 2024 formed with disks, and these disks still exist at the present time. In addition, all but one of the disk sources identified in our survey lie in the infrared excess region of the JHKL color-color diagram for the cluster. This demonstrates that JHKL color-color diagrams are extremely efficient in identifying YSOs with disks. Of the 14 sources with K - L colors suggestive of protostellar objects, \~29% are protostellar in nature, while ~7% are true Class I YSOs. This may be due to extinction producing very red K - L colors in Class II YSOs, thus making them appear similar in color to protostars. This suggests caution must be applied when estimating the sizes and lifetimes of protostellar populations within star forming regions based on K - L colors alone. Finally, we calculate the luminosities of the Class II YSOs in NGC 2024, rho Oph and Taurus and discuss the results.

The LBDS Hercules sample of mJy radio sources at 1.4 GHz -- I. Multicolour photometry

The results are presented of an extensive programme of optical and infrared imaging of radio sources in a complete subsample of the Leiden–Berkeley Deep Survey. The LBDS Hercules sample consists of 72 sources observed at 1.4 GHz, with flux densities S1.41.0 mJy, in a 1.2 deg2 region of Hercules. This sample is almost completely identified in the g, r, i and K bands, with some additional data available at J and H. The magnitude distributions peak at r≃22 mag, K≃16 mag and extend down to r≃26 mag, K≃21 mag. The K-band magnitude distributions for the radio galaxies and quasars are compared with those of other radio surveys. At S1.4 GHz≲1 Jy, the K-band distribution does not change significantly with radio flux density. The sources span a broad range of colours, with several being extremely red (r−K≳6). Though small, this is the most optically complete sample of mJy radio sources available at 1.4 GHz, and is ideally suited for studying the evolution of the radio luminosity function out to high redshifts.

Infrared spectroscopy of cataclysmic variables -- III. Dwarf novae below the period gap and nova-like variables

We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK Lyn, T Leo, SW UMa and WZ Sge, the nova-like variables DW UMa, V1315 Aql, RW Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral types ranging from K2 to M6. The spectra of the dwarf novae are dominated by emission lines of H i and He i. The large velocity and equivalent widths of these lines, in conjunction with the fact that the lines are double-peaked in the highest inclination systems, indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which we obtained time-resolved data covering a complete orbital cycle, the emission lines show modulations in their equivalent widths that are most probably associated with the bright spot (the region where the gas stream collides with the accretion disc). There are no clear detections of the secondary star in any of the dwarf novae below the period gap, yielding upper limits of 10–30 per cent for the contribution of the secondary star to the observed K-band flux. In conjunction with the K-band magnitudes of the dwarf novae, we use the derived secondary star contributions to calculate lower limits to the distances to these systems. The spectra of the nova-like variables are dominated by broad, single-peaked emission lines of H i and He i– even the eclipsing systems we observed do not show the double-peaked profiles predicted by standard accretion disc theory. With the exception of RW Tri, which exhibits Na i, Ca i and 12CO absorption features consistent with a M0V secondary contributing 65 per cent of the observed K-band flux, we find no evidence for the secondary star in any of the nova-like variables. The implications of this result are discussed.

Spiral galaxy distance indicators based on near-infrared photometry

We compare two methods of distance determination to spiral galaxies using optical/near-infrared (NIR) observations, the (I-K) versus M_K colour - absolute magnitude (CM) relation and the I and K-band Tully-Fisher relation (TFR). Dust-free colours and NIR absolute magnitudes greatly enhance the usefulness of the NIR CM relation as a distance indicator for moderately to highly inclined_spiral_ galaxies_in the field_ (inclinations between ~ 80 and 90 deg); by avoiding contamination by dust the scatter in the CM relation is significantly reduced, compared to similar galaxy samples published previously. The CM relation can be used to determine distances to field spiral galaxies with M_K > -25.5, to at least M_K ~ -20. Our results, supplemented with previously published observations for which we can - to some degree - control the effects of extinction, are consistent with a universal nature of the CM relation for field spiral galaxies. High-resolution observations done with the Hubble Space Telescope can provide a powerful tool to calibrate the relation and extend the useful distance range by more than a factor of 2 compared to ground-based observations. The intrinsic scatter in the NIR CM relation in the absolute K-band magnitudes is ~0.5 mag, yielding a lower limit to the accuracy of distance determinations on the order of 25%. Although we find an unusually low scatter in the TFR (probably a statistical accident), a typical scatter in the TFR would yield distances to our sample galaxies with uncertainties of only about 15%. However, one of the main advantages of the use of the NIR CM relation is that_we only need photometric data_ to obtain distance estimates; use of the TFR requires additional kinematic data, although it can be used to significantly greater distances.

A Prediction of Brown Dwarfs in Ultracold Molecular Gas

A recent model for the stellar initial mass function (IMF), in which the stellar masses are randomly sampled down to the thermal Jeans mass from hierarchically structured pre-stellar clouds, predicts that regions of ultra-cold CO gas, such as those recently found in nearby galaxies by Allen and collaborators, should make an abundance of Brown Dwarfs with relatively few normal stars. This result comes from the low value of the thermal Jeans mass, considering that the hierarchical cloud model always gives the Salpeter IMF slope above this lower mass limit. The ultracold CO clouds in the inner disk of M31 have T~3K and pressures that are probably 10 times higher than in the solar neighborhood. This gives a mass at the peak of the IMF equal to 0.01 Msun, well below the Brown Dwarf limit of 0.08 Msun. Using a functional approximation to the IMF, the ultracold clouds would have 50% of the star-like mass and 90% of the objects below the Brown Dwarf limit. The brightest of the Brown Dwarfs in M31 should have an apparent, extinction-corrected K-band magnitude of ~21 mag in their pre-main sequence phase.

The Nature and Evolutionary History of GRO J1744−28

GRO J1744-28 is the first known X-ray source to display bursts, periodic pulsations, and quasi-periodic oscillations. This source may thus provide crucial clues that will lead to an understanding of the differences in the nature of the X-ray variability from various accreting neutron stars. The orbital period is 11.8 days, and the measured mass function of 1.31 x 10(exp -4) solar mass is one of the smallest among all known binaries. If we assume that the donor star is a low-mass giant transferring matter through the inner Lagrange point, then we can show that its mass is lower than approximately 0.7 solar mass and probably closer to 0.25 solar mass. Higher mass, but unevolved, donor stars are shown to be implausible. We also demonstrate that the current He core mass of the donor star lies in the range of 0.20-0.25 solar mass. Thus, this system is most likely in the final stages of losing its hydrogen-rich envelope, with only a small amount of mass remaining in the envelope. If this picture is correct, then GRO J1744-28 may well represent the closest observational link that we have between the low-mass X-ray binaries and recycled binary pulsars in wide orbits. We have carried out a series of binary evolution calculations and explored, both systematically and via a novel Monte Carlo approach, the range of initial system parameters and input physics that can lead to the binary parameters of the present-day GRO J1744-28 system. The input parameters include both the initial total mass and the core mass of the donor star, the neutron-star mass, the strength of the magnetic braking, the mass-capture fraction, and the specifics of the core mass/radius relation for giants. Through these evolution calculations, we compute probability distributions for the current binary system parameters (i.e., the total mass, core mass, radius, luminosity, and K-band magnitude of the donor star, the neutron star mass, the orbital inclination angle, and the semimajor axis of the binary). Our calculations yield the following values for the GRO J1744-28 system parameters (with 95% confidence limits in parentheses): donor star mass: 0.24 solar mass (0.2-0.7 solar mass); He core mass of the donor star: 0.22 solar mass (0.20-0.25 solar mass); neutron-star mass: 1.7 solar mass (1.39-1.96 solar mass); orbital inclination angle: 18deg (7deg-22deg); semi- major axis: 64 lt-s (60-67 lt-s); radius of the donor star: 6.2 solar radius(6-9 solar radius); luminosity of donor star: 23 solar luminosity (15-49 solar luminosity), and long-term mass transfer rate at the current epoch: 5 x 10(exp -10)solar mass/yr (2 x 10(exp -10) to 5 x 10(exp -9)solar mass/yr). We deduce that the magnetic field of the underlying neutron star lies in the range of approximately 1.8 x 10(exp 11)G to approximately 7 x 10(exp 11)G, with a most probable value of 2.7 x 10(exp 11)G. This is evidently sufficiently strong to funnel the accretion flow onto the magnetic polar caps and suppress the thermonuclear flashes that would otherwise give rise to the type 1 X-ray bursts observed in most X-ray bursters. We present a simple paradigm for magnetic accreting neutron stars where X-ray pulsars, GRO J1744-28, the Rapid Burster, and the type 1 X-ray bursters may form a continuum of possible behaviors among accreting neutron stars, with the strength of the neutron-star magnetic field serving as a crucial parameter that determines the mode of X-ray variability from a given object.

On Calibrating Brightest Asymptotic Giant Branch Stars as Age Indicators: The Bulge Globular Cluster NGC 6553 and the Age of M32

Bright asymptotic giant branch (AGB) stars can be used as an age indicator for stellar populations that are too far away for their main-sequence turnoffs to be reachable. However, the method requires an empirical calibration, as the brightness of the AGB termination depends on both age and metallicity in ways that cannot be predicted from first principles. In this Letter, we present an attempt at providing such a calibration for old, near-solar metallicity populations. For this purpose, we use the bulge, metal-rich globular cluster NGC 6553, combining available Hubble Space Telescope (HST) optical photometry with near-IR data. HST observations have indicated the cluster to be nearly as old as halo globular clusters (Ortolani et al.), and here we use the same data to determine the reddening and distance of the cluster. When we combine these observations with the IR data, we obtain the absolute K-band and bolometric magnitudes of the brightest AGB stars in the cluster. It turns out that these brightest stars are nearly as bright as the brightest AGB stars in the dwarf elliptical galaxy M32, and we conclude that no appreciable age difference between the globular cluster and M32 is required to account for the brightest stars in this galaxy.

An optically luminous radio galaxy at Z = 3.22 and the K-z diagram at high redshift

view Abstract Citations (61) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Optically Luminous Radio Galaxy at Z = 3.22 and the K-z Diagram at High Redshift Eales, Stephen A. ; Rawlings, Steve ; Dickinson, Mark ; Spinrad, Hyron ; Hill, Gary J. ; Lacy, Mark Abstract We present images of the z = 3.22 radio galaxy 6C 1232 + 39 taken through the B, R, J, J, H, and K filters, an image taken through a narrow-band filter centered on the Lyα line, and an image made with the VLA at 5 GHz. Unlike the two other z > 3 radio galaxies that have been extensively studied (B2 0902 + 34 and 4C 41.17), this radio galaxy has a "classical double" radio structure. The structure of the radio galaxy is a strong function of wavelength, changing from a long linear structure at the shortest wavelength (B) to one that is dominated by a single compact component at the longest wavelength (K). The galaxy's optical, emission-line, and radio structures are closely aligned; apart from the overall alignment, there is, however, not the clear correspondence between the continuum and Lyα structures that would be expected if both trace the same young starburst regions. We show that, like the two other well-studied z > 3 radio galaxies, 6C 1232 + 39 has a red bump in its rest-frame optical spectrum. Low scatter in the K-z diagram is often cited as evidence that radio galaxies formed early in the history of the universe. We show that there is now some evidence that the scatter in the K-z diagram at z > 2 is greater than the scatter at z < 2. We discuss briefly the possible causes of this increased scatter, noting that near-infrared spectroscopy will be crucial in determining whether the increased scatter gives any useful information about the epoch at which radio galaxies formed. Finally we argue that the dispersion in the K-band magnitudes of the known z > 2 radio galaxies, and in particular the existence of luminous objects like 6C 1232+39, calls into question the use of the K-z Hubble relation to estimate the redshifts of distant radio galaxies from K magnitudes alone, a method that underpins the only published evidence for a redshift cutoff for radio galaxies. Publication: The Astrophysical Journal Pub Date: June 1993 DOI: 10.1086/172688 Bibcode: 1993ApJ...409..578E Keywords: Galactic Evolution; Radio Galaxies; Red Shift; Visual Observation; Infrared Imagery; Lyman Alpha Radiation; Spectral Energy Distribution; Astrophysics; GALAXIES: EVOLUTION; GALAXIES: STELLAR CONTENT; RADIO CONTINUUM: GALAXIES full text sources ADS | data products SIMBAD (3) NED (1)

High-luminosity carbon stars in the galactic anticenter

view Abstract Citations (40) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Luminosity Carbon Stars in the Galactic Anticenter Jura, M. ; Joyce, R. R. ; Kleinmann, S. G. Abstract K-band magnitudes of 211 carbon stars in the Galactic anticenter are presented. The surface density, brightness range, and observed colors of stars in the sample are discussed. It is suggested that the K-band extinction gradient in the Galactic plane near l = 180 deg is between 0.15 and 0.3/kpc. In contrast to the total density of stars, it is found that the density of high-luminosity carbon stars does not decrease in the anticenter region out to at least 3 kpc from the sun. It is proposed that this is due to the fact that lower metallicity stars spend more time as carbon stars compared to stars of solar metallicity. Also, it is shown that the average mass-loss rates from high-luminosity carbon stars in the anticenter direction appear to be lower by a factor of 1.7 than those for carbon stars in the solar neighborhood. Publication: The Astrophysical Journal Pub Date: January 1989 DOI: 10.1086/167062 Bibcode: 1989ApJ...336..924J Keywords: Carbon Stars; Milky Way Galaxy; Sky Surveys (Astronomy); Stellar Luminosity; Metallicity; Radiation Pressure; Solar Neighborhood; Spatial Distribution; Spectral Bands; Stellar Magnitude; Astrophysics; STARS: CARBON; STARS: EVOLUTION; STARS: MASS LOSS; STARS: STELLAR STATISTICS full text sources ADS | data products SIMBAD (214)

Gamma-ray burster counterparts - Infrared

The discovery of an IR counterpart to a gamma-ray burster (GRB) would be a big step forward in understanding this enigmatic phenomenon. A program of searching for IR emission from the smallest GRB source regions has been initiated. Seven boxes have been searched with ground-based telescopes at a wavelength of 2.2 microns and 23 with the IRAS data base at wavelengths of 12, 25, 60, and 100 microns. No convincing candidates were identified. The most constraining result are for two error boxes where the K-band magnitude are found to be fainter than 19.03. This observation is compared with the flux predicted from either a companion star or an accretion disk. The new IR observations pose serious difficulties for several GRB models.