Anticenter Direction Research Articles

Chemical abundances of planetary nebulae towards the Galactic anticenter

In this paper we report new observations and derive chemical abundances for a sample of 26 planetary nebulae (PN) located in the anticenter direction. Most of these nebulae are far away objects, located at Galactocentric distances greater than about 8 kpc, so that they are particularly useful for the determination of the radial gradients at large distances from the galactic center. A comparison of the present results with previously determined abundances suggests that the radial abundance gradients flatten out at distances larger than about 10 kpc from the center.

Discovery of three optical open clusters in the Galaxy

We report the discovery of three optical open clusters in the Milky Way. Two clusters are in Scutum (Cluster 1 at � = 18.44 ◦ and b = −0.42 ◦ , and Cluster 2 at � = 19.60 ◦ and b = −1.02 ◦ ), thus projected not far from the Galactic center direction, and the other is in Canis Major (Cluster 3 at � = 235.61 ◦ and b = −4.10 ◦ ), near the anti-center direction. Cluster 3 is less populous than Clusters 1 and 2, but presents evidence of being a physical system. The objects were found optically by inspecting maps obtained from the Guide Star Catalogue and images from the Digitized Sky Survey. No previous identification of a cluster has been reported in any of these areas so far. The analysis was carried out with 2MASS photometry in J and H. For Cluster 1 we derive an age of t = 25 ± 5 Myr, a reddening E(B − V) = 2.18 ± 0.03 and a distance from the Sun d� = 1.64 ± 0.19 kpc; for Cluster 2, t = 500 ± 100 Myr, E(B − V) = 0.91 ± 0.03 and d� = 2.19 ± 0.21 kpc; finally for Cluster 3, t = 32−100 Myr, E(B − V) = 0.94 ± 0.03 and d� = 3.93 ± 0.35 kpc. Luminosity and mass functions are derived for Clusters 1 and 2 which, in turn, allow us to estimate their observed masses as 147 Mand 89 M� , respectively. Estimated total masses, by extrapolating the mass functions to 0.08 M� , amount to 382 Mand 614 Mfor the two clusters. Cluster 3 has an observed mass of ∼55 M� . The present results indicate that further searches in the optical might still reveal new open clusters, especially in the infrared bands.

The relatively young, metal-poor and distant open cluster NGC 2324

We have obtained CCD photometry in the Johnson V, Kron-Cousins I and CT1 Washington systems for NGC 2324, a rich open cluster located ∼35 ◦ from the Galactic anticentre direction. We measured V magnitudes and V − I colours for 2865 stars and T1 magnitudes and C − T1 colours for 1815 stars in an area of 13. 6 × 13. 6. The comparison of the cluster colour-magnitude diagrams with isochrones of the Geneva group yield E(V − I) = 0.33 ± 0.07 and V − MV = 13.70 ± 0.15 for log t = 8.65 (t = 440 Myr) and Z = 0.008 ((Fe/H) = −0.40), and E(C − T1) = 0.40 ± 0.10 and T1 − MT 1 = 13.65 ± 0.15 for the same age and metallicity level. The resulting E(V − I) reddening value implies E(B − V) = 0.25 ± 0.05 and a distance from the Sun of (3.8 ± 0.5) kpc. Star counts carried out within and outside the cluster region allowed us to estimate the cluster angular radius as 5. 3 ± 0. 3 (5.9 pc). When using the E(B − V) reddening value here derived and the original Washington photometric data of Geisler et al. (1991) for the stars confirmed as red cluster giants from Coravel radial velocities, we found (Fe/H) = −0.31 ± 0.04, which is in good agreement with the best fits of isochrones. Therefore, NGC 2324 is found to be a relatively young, metal-poor and distant open cluster located beyond the Perseus spiral arm. A comparison of NGC 2324 with 10 well-known open clusters of nearly the same age shows that the cluster metal abundance and its position in the Galaxy are consistent with the existence of a radial abundance gradient of −0.07 dex kpc −1 in the Galactic disc.

Halo Structure Shown by RR Lyrae Stars in the Anticenter Direction

Newberg et al., Yanny et al., Ibata et al., Rocha-Pinto et al., and Martin et al. have reported overdensities of stars that form a ring with a galactocentric distance (Rgal) of ≲18 kpc. Martin et al. and Frinchaboy et al. have found star clusters associated with these overdensities; Martin et al. found what seems to be the central overdensity in Canis Major, so we shall refer to it as the CMa ring. The stars in the CMa ring have a small velocity dispersion and [Fe/H] of about -0.4 and -1.6, respectively. Zinn et al. found a small RR Lyrae overdensity in the more populous southern arc of the CMa ring. We do not find any overdensity of RR Lyrae stars in a 65 deg2 field that covers a more tenuous part of the ring in the anticenter. Existing evidence suggests that the halo component of the CMa ring has a horizontal-branch (HB) morphology that does not favor RR Lyrae stars; the evidence from the associated clusters suggests that it may be richer in blue HB stars. Our RR Lyrae sample in the anticenter contains three groups (each containing three stars that have a high probability of physical association). These groups account for half of the RR Lyrae stars with 17 kpc ≤ Rgal ≤ 28 kpc in this field; all of these RR Lyrae stars are of Oosterhoff I type. It is suggested that they may be globular cluster remnants.

NGC 1883: a neglected intermediate-age open cluster located in the outskirts of the Galactic disc

We report on BVI CCD photometry of a field centred in the region of the open cluster NGC 1883, down to V = 21. This cluster has never been studied so far; we provide, for the first time, estimates of its fundamental parameters ‐ namely radial extent, age, distance and reddening. We find that the cluster has a radius of about 2.5 arcmin, and shows signatures of dynamical relaxation. NGC 1883 is located in the anticentre direction, and exhibits a reddening in the range E(B − V ) = 0.23‐0.35, depending on the metal abundance. It turns out to be of intermediate age (1 Gyr old), and is quite distant for an open cluster. In fact, it is located 4.8 kpc from the Sun, and more than 13 kpc from the Galactic centre. This results makes NGC 1883 one of the most peripheral old open clusters, with important consequences for the trend of the metallicity with distance in the outer Galactic disc.

The relatively young and metal-poor Galactic open cluster NGC 2194

We present CCD VIKC photometry down to V≈ 21 mag in the field of the rich open cluster NGC 2194, which is projected towards the Galactic anticentre direction. We measured V magnitudes and V−I colours for a total of 2515 stars in a field of 13.6 × 13.6 arcmin2. These data are supplemented with CCD photometry in the C, M and T1 filters of the Washington system and photoelectric CMT1T2 photometry of 20 red giant candidates. Based on the best fits of isochrones computed by the Geneva and Padova groups to the (V, V−I) colour — magnitude diagram, we derive a colour excess E(V−I) = 0.75, a cluster distance of 3.2 kpc and an age of 400 Myr. Five independent Washington abundance indices yield a mean cluster metallicity of [Fe/H]=−0.27 ± 0.06, which is compatible with the existence of both a radial and Z gradient in the Galactic disc. NGC 2194 is a relatively young open cluster, whose deficiency in metal content can be accounted for by the fact that it was born not only far from the Galactic centre in the outer disc, but also at a relatively high Z value.

One ring to encompass them all: a giant stellar structure that surrounds the Galaxy

We present evidence that the curious stellar population found by the Sloan Digital Sky Survey in the Galactic anticentre direction extends to other distant fields that skirt the plane of the Milky Way. New data, taken with the Isaac Newton Telescope Wide Field Camera, show a similar population, narrowly aligned along the line of sight, but with a galactocentric distance that changes from similar to15 to similar to20 kpc (over similar to100degrees on the sky). Despite being narrowly concentrated along the line of sight, the structure is fairly extended vertically out of the plane of the disc, with a vertical scaleheight of 0.75 +/- 0.04 kpc. This finding suggests that the outer rim of the Galaxy ends in a low surface brightness stellar ring. Presently available data do not allow us to ascertain the origin of the structure. One possibility is that it is the wraith of a satellite galaxy devoured long ago by the Milky Way, although our favoured interpretation is that it is a perturbation of the disc, possibly the result of ancient warps. Assuming that the ring is smooth and axisymmetric, the total stellar mass in the structure may amount to similar to2 x 10(8) M. up to similar to10(9) M(.).

Old open clusters: the interesting case of Berkeley 21

ABSTRACT We present CCD BVI photometry of the old open cluster Berkeley 21, one of themost distant clusters in the Galactic anticentre direction, and possibly the lowestmetallicity object in the open clusters sample. Its position and metal abundance makeit very important for the study of the Galactic disc.Using the synthetic Colour - Magnitude Diagram method, we estimate values fordistance modulus (m-M) 0 = 13.4–13.6, reddening E(B−V)= 0.74–0.78 (with possibledifferential absorption), and age = 2.2–2.5 Gyr.Key words: Hertzsprung-Russell (HR) diagram – open clusters and associations:general – open clusters and associations: individual: Berkeley 21 1 INTRODUCTIONOld open clusters cover a large range of distances, metal-licities, and ages (Friel 1995), and that warrants their usein investigations of the chemical and dynamical evolution ofour Galaxy. To study the metallicity and age distribution ofopen clusters with Galactocentric distance, and avoid unnec-essary and dangerous biases, a key requisite is homogenousanalysis of very accurate observational data, as discussed by,e.g, Janes & Phelps (1994, JP94) Carraro & Chiosi (1994,CC94), Friel (1995), Twarog et al. (1997,TAAT97).This is the fifth paper of a series dedicated to the exami-nation of old open clusters of different ages and metallicities,and located at different Galactic radii: for them we measurein a homogenous way distance, age, reddening and metal-licity. These quantities are derived from comparison of theobserved colour-magnitude diagrams (CMDs) to syntheticones generated by a numerical code based on stellar evolu-tion tracks and taking into account theoretical and obser-vational uncertainties (Tosi et al. 1991). These simulationsare much more powerful than the classical isochrone fittingmethod to study the evolutionary status of the analysedregion and have been successfully applied both to nearby ir-regular galaxies (Greggio et al. 1998 and references therein)and to galactic open clusters (NGC2243: Bonifazi et al. 1990;Cr261: Gozzoli et al. 1996; NGC6253: Bragaglia et al. 1997;NGC2506: Marconi et al. 1997).Berkeley 21 (Be21) is located toward the Galactic an-ticentre, at coordinates RA(1950) = 5:48:42, DEC(1950)= 21:46, and l

Progress on Establishing the Spatial Distribution of Material Responsible for the \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\frac{1}{4}$ \end{document} keV Soft X‐Ray Diffuse Background Local and Halo Components

In this paper we present a new look at the distribution of emission responsible for the soft X-ray diffuse background (SXRB) using ROSAT all-sky survey data. This is prompted by the demonstration of the existence of extensive 1/4 keV emission in the Galactic halo that was not considered in the most successful previous model, in which the bulk of the observed 1/4 keV X-rays originated in a Local Hot Bubble (LHB) that surrounds the Sun. The basic distribution can be represented by two angularly varying Galactic components (the LHB and an X-ray halo) and an isotropic extragalactic component. In addition, there are the distinct enhancements of supernova remnants, superbubbles, and clusters of galaxies. Using the negative correlation between the SXRB and DIRBE-corrected IRAS 100 μm intensity, we find a LHB that is similar to previous models, although it is possibly more limited in extent. The emission of the LHB varies by a factor of ~3.3 with direction and produces ROSAT 1/4 keV intensities between ~250 and ~820 × 10-6 counts s-1 arcmin-2 (typically brighter at higher Galactic latitudes), with inferred emission measures of ~0.0018 to 0.0058 cm-6 pc (assuming thermal ionization equilibrium). The distribution of the emission temperature of the LHB is peaked at 106.07 K with a range of ±12% at FWHM. While this variation is small and is perhaps due to systematic uncertainties in the analysis, there is a suggestion of a cooler region in the anticenter direction consistent with previous studies. We derive halo plus extragalactic intensities that vary from ~400 to 3000 × 10-6 counts s-1 arcmin-2 outside the absorbing gas of the Galactic disk. As the low end of the range is comparable to what is expected for the extragalactic background, this implies that the halo emission varies considerably over the sky, with inferred emission measures ranging from near zero to >0.02 cm-6 pc. The distribution of emission temperatures in the halo, again derived from thermal equilibrium emission models, peaks near 106.02 K and varies over ±20% at FWHM.

Schmidt plate survey in the Galactic centre and anticentre direction. Luminosity and mass functions of open clusters

AbstractThe proper motions and stellar magnitudes for more than 20 000 stars distributed in areas around eight open clusters in the directions of the Sagittarius‐Carina and Perseus spiral arms were used to determine the cluster membership. Both spatial‐kinematical and statistical criteria were used for member seletion. The luminosity functions of cluster members were constructed and used for the further data improvement. The safest portions of the luminosity function free both from evolved stars and faint field star contamination were used for mass function construction. The composite mass function was derived from the data on five young clusters with log t < 8.2. A dependence of the mass function slope on the adopted input parameters (mass‐luminosity relation and distance scale) and on member selection procedure was tested. The slope was found to vary in a range from 1.36 to 1.80 for lg M/M⊙ between 0.3 and 1.2. A possible relation between the individual MF slopes and cluster ages was indicated. The results are in good agreement with published data.

Investigation of Galactic Structure with Denis Star Counts

Thanks to the DENIS program (Deep Near-Infrared Survey of the Southern Sky), relatively deep near-infrared star counts are now available for the first time on a large scale. The basic method to interpret star counts in terms of galactic structure is to compare them with predictions given by models of the point source sky. Of particular promise are studies with DENIS of the spatial distribution of evolved stars in our Galaxy, thanks to its high sensitivity to red giant and to the much lower interstellar extinction that hampers visual observations of far-away stars in the disc of our Galaxy. In this paper, I present a sample of extensive comparisons between two models of the Galaxy and DENIS star counts (Ruphy 1996). I will focus on the analysis of star counts in the anticenter direction, that leads to new values for the distance of the cutoff and the radial scale length of the stellar disc.

Computer models of the Sagittarius dwarf interaction with the Milky Way

The interaction between the dwarf galaxy in Sagittarius and the Milky Way Galaxy has been modelled with a parallel computer implementation of an N-body treecode. Models are made that reproduce the observed position, size, velocity, proper motion and velocity gradient of the dwarf in its likely pre-disc encounter, and other models are studied in which the dwarf has just passed through the disc. Several observable differences between these cases are found. In the pre-collision case, the dwarf is bound to the Milky Way and it passed through the disc previously 1.7 x 108 yr ago in the anticentre direction. It will cross through the disc again in 3.5 x 10 7 yr. Each disc crossing spins up the dwarf core and tidally stretches its outer envelope, leaving the core slightly less bound. If such disc crossings are common for dwarfs near large galaxies, then the likely removal of gas from the dwarf at each crossing, combined with the observed high dark matter fraction for most dwarfs, implies that dark matter is not in the form of undetected cold gas. In the preferred model, the outer envelope of the dwarf includes the positions and velocities of the globular clusters NGC 6715, Terzan 7, Terzan 8 and Arp 2, which implies that these clusters could be fragments of a previously larger system. They could also be old detached star formation cores that formed in the Sagittarius dwarf during previous disc crossings.

Schmidt survey in the Galactic anticentre direction. 1. Investigation of open clusters

AbstractA study of four open clusters in the direction of the Galactic anticentre (l = 186°, b = +2°) is presented. In a field of 8.32 square degrees proper motions and B magnitudes for about 79 000 stars down to 19.5 were determined on Tautenburg Schmidt plates. For more than 15 500 of them U magnitudes down to 17.3 could be obtained. Additionally, OCA Schmidt plates were used to determine V, R magnitudes in a larger field of 24.45 square degrees for 271 000 stars down to V = 18.2. For stars brighter than V = 15.5 an accuracy of about 1.5 mas/yr has been estimated for proper motions. The rms errors of stellar magnitudes and colour indices are 0.09 – 0.12 mag.Several open clusters have been already known in this direction of the sky, e.g. NGC 2168 or M 35 (C 0605+243), NGC 2158 (C 0604+241) and IC 2157 (C 0601+240). Inspecting the plates and analysing the colour‐magnitude diagrams and published data, we could identify an additional anonymous cluster C 0605+242 with a projection on the sky near the centre of M 35 but at a larger distance from the Sun.The cluster membership determination was carried out using information on spatial and proper motion distributions of stars in the field. The colour‐magnitude diagrams were derived down to the limiting stellar magnitude. For each cluster the interstellar extinction Av, the diameters of the core and corona, the ages and spatial velocity components (V,W) relative to the LSR in the Y,Z – Galactic directions were determined.The distances to the clusters of 960 pc, 2 600 pc, 2 520 pc and 3 700 pc were obtained for M 35, IC 2157, C 0605+242 and NGC 2158. They show the loci of the clusters in the Local and Perseus spiral arms and at external border of Perseus arm, respectively.

SiO Maser Sources in the Outer Disk of the Galaxy

view Abstract Citations (42) References (59) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SiO Maser Sources in the Outer Disk of the Galaxy Jiang, B. W. ; Deguchi, S. ; Yamamura, I. ; Nakada, Y. ; Cho, S. H. ; Yamagata, T. Abstract The observations in the 28SiO j = 1-0 V = 1, J = 1-0 V = 2 lines and the 29SiO j = 1-0, V = 0 lines were simultaneously made toward 181 color-selected IRAS sources in the outer disk of the Galaxy (at longitudes between 90° and 250°). The 28SiO lines were detected in 63 sources (56 new) and the 29SiO line in 11 sources (9 new). Most of the detections are optically variable stars, mainly Mira-type variables and a few semiregular variables. The detection rate (35%) is much lower than that of the bulge survey performed by the same observational system the 45 m telescope at Nobeyama Radio Observatory. The lower detection rate of SiO maser emission is partly attributed to the increase of contaminations by stars with C-rich circumstellar envelopes and young stellar objects in the outer disk sample. The kinematical implications of the observational results are also discussed. The luminosity distances to the SiO maser sources are estimated from their IRAS fluxes at 12 μm and colors. By combining the SiO radial velocity and the luminosity distance, the rotation curve of the outer Galactic disk is found to be slightly falling within the Galactocentric distance between 8.5 and 12 kpc. The sources located within 20° from the Galactic anticenter direction are used to check for a peculiar motion of the local standard of rest. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1996 DOI: 10.1086/192345 Bibcode: 1996ApJS..106..463J Keywords: GALAXY: KINEMATICS AND DYNAMICS; ISM: MOLECULES; MASERS; STARS: VARIABLES: OTHER LONG-PERIOD VARIABLES full text sources ADS | data products SIMBAD (182) CDS (2) Related Materials (1) Catalog: 1997yCat..21060463J

How do the Stellar Disc and Thick Disc Stop?

As part of a stellar population sampling program, a series of photometric probes at various field sizes and depths have been obtained in a low extinction window in the galactic anticentre direction. Very deep CCD frames probe the most external parts of the disc, providing strong evidence that the galactic density scale length for the old disc population is rather short (2.5 kpc) and drops abruptly beyond 5.5-6 kpc.Deeper frames in the I band allow to estimate photometric distances and confirm the position of the disk edge. A few stars are found at larger distances. Their number is exactly what we expect if the thick disk does not have any cutoff. We discuss the implications for the formation and evolution of the disc, for the star formation threshold, and for the origin of the thick disc population.

UBV (RI)C-H photometry and GRISM spectroscopy of the young cluster Bochum 2 in the anticentre direction

UBV(RI)C–Hα CCD photometry and GRISM spectroscopy are presented for Bochum 2, a distant cluster in the galactic anticentre direction. The cluster is young, with late O-type members still on the main sequence. No red giant/supergiant is associated with the cluster. 28 possible cluster members are identified. The distance and mean reddening are ~ 6 kpc and E(B – V) = 0.80, respectively. The reddening law for Bochum 2 matches the standard one. The upper main sequence of the cluster is well defined over a range ≥ 6.5 mag, with some spread due to differential reddening. No strong emission line or Wolf-Rayet star has been detected. There is no bright H II region associated with the cluster.

A Complete, Multicolour Survey of Absolute Proper Motions in the Anticentre Direction at Intermediate Latitude: Kinematics of the Galaxy's Stellar Populations

We present the observational results of UBV photometry and absolute proper motions in the anticentre direction at intermediate latitude (l = 167.5°, b = 47.4°) for an 8.6 square degree field. The sample is complete down to V = 17, and the accuracy of the proper motions is better than per century for stars brighter than V = 16. It is attempted here to make an investigation of the structure and kinematics of the Galaxy from absolute proper motions. Details of the present work can be found elsewhere (Ojha et al. 1993).

The edge of the Galactic disk

view Abstract Citations (84) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Edge of the Galactic Disk Robin, Annie C. ; Creze, Michel ; Mohan, Vijay Abstract As part of a stellar population sampling program, a series of photometric probes at various field sizes and depths have been obtained in a low extinction window in the galactic anticentre direction. Such data set strong constraints on the radial structure of the disc. At the forefront of this "drilling" program, very deep CCD frames probe the most external parts of the disc. Over the whole effective magnitude range (18 to 25), all contributions in the statistics which should be expected from old disc stars beyond 6 kpc vanish, although such stars dominate by far at distances less than 5 kpc. This is the signature of a sharp cut-off in the star density: the edge of the galactic disc between 5.5 and 6 kpc. As a consequence, the galactic radius does not exceed 14 kpc (assuming $R/-/(//sun/)$=8.5). Colours of elliptical galaxies measured in the field rule out the risk of being misled by undetected extinction. Publication: The Astrophysical Journal Pub Date: November 1992 DOI: 10.1086/186640 arXiv: arXiv:astro-ph/9210001 Bibcode: 1992ApJ...400L..25R Keywords: Galactic Structure; Milky Way Galaxy; Star Distribution; Astronomical Photometry; Charge Coupled Devices; Star Formation; Stellar Magnitude; Astrophysics; GALAXY: STRUCTURE; GALAXY: STELLAR CONTENT; Astrophysics E-Print: 8 pages, Besancon Observatory preprint n. 2 full text sources arXiv | ADS |

Cool Supergiants in the Solar Neighborhood

We have identified 21 mass-losing red supergiants (20 M-type, 1 G-type, L > 105 L⊙) within 2.5 kpc of the Sun. These supergiants are highly evolved descendants of main sequence stars with initial masses larger than about 20 M⊙. The surface density projected onto the plane of the Milky Way is between about 1 and 2 kpc–2. Although with considerable uncertainty, we estimate that the mass return by the M supergiants is somewhere between 1 and 3 10-5 M⊙ kpc–2 yr–1. In the hemisphere facing the galactic center there is much less mass loss from M supergiants than from W-R stars, but in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 2 and 4 105 years. During this phase a star of initially at least 20 M⊙ returns perhaps 3 to 10 M⊙ into the interstellar medium.

Particle Acceleration in the Disk-Halo System

The recent observations of the nonthermal properties of the halo of our Galaxy at radio and γ-ray wavelengths are summarized. Radio and γ-ray data show a similar spectral flattening with Galactic height towards the anticenter direction, which is interpreted as a cosmic-ray effect. Several theoretical explanations for the flattening of the energy spectra of the radiating cosmic-ray electrons (in the radio) and nucleons (in γ-rays) are reviewed including propagation of cosmic rays in an accelerating Galactic wind and the presence of cosmic-ray sources with flat energy spectra in the halo.