Local Group Dwarf Elliptical Galaxies Research Articles

Resolving the Nuclear Radio Emission from M32 with the Very Large Array

Abstract The Local Group dwarf elliptical galaxy M32 hosts one of the nearest and most under-luminous supermassive black holes (SMBHs) ever known, offering a rare opportunity to study the physics of accreting SMBHs at the most quiescent state. Recent Very Large Array (VLA) observations detected a radio source at the nucleus of M32, which was suggested to be the radio counterpart of the SMBH. To further investigate the radio properties of this nuclear source, we have conducted follow-up, high-resolution VLA observations in four epochs between 2015 and 2017, each with dual frequencies. At 6 GHz, the nuclear source is resolved under an angular resolution of ∼0.″4, exhibiting a coreless, slightly lopsided morphology with a detectable extent of ∼2.″5 (∼10 pc). No significant variability can be found among the four epochs. At 15 GHz, no significant emission can be detected within the same region, pointing to a steep intrinsic radio spectrum (with a 3σ upper limit of −1.46 for the spectral index). We discuss possible scenarios for the nature of this nuclear radio source and conclude that a stellar origin, in particular, planetary nebulae, X-ray binaries, supernova remnants, or diffuse ionized gas powered by massive stars, can be ruled out. Instead, the observed radio properties can be explained by synchrotron radiation from a hypothetical wind driven by the weakly accreting SMBH.

A Chandra Survey of Milky Way Globular Clusters. I. Emissivity and Abundance of Weak X-Ray Sources

Abstract Based on archival Chandra data, we have carried out an X-ray survey of 69, or nearly half the known population of, Milky Way globular clusters (GCs), focusing on weak X-ray sources, mainly cataclysmic variables (CVs) and coronally active binaries (ABs). Using the cumulative X-ray luminosity per unit stellar mass (i.e., X-ray emissivity) as a proxy of the source abundance, we demonstrate a paucity (lower by 41% ± 27% on average) of weak X-ray sources in most GCs relative to the field, which is represented by the Solar Neighborhood and Local Group dwarf elliptical galaxies. We also revisit the mutual correlations among the cumulative X-ray luminosity (L X), cluster mass (M), and stellar encounter rate (Γ), finding , and . The three quantities can further be expressed as , which indicates that the dynamical formation of CVs and ABs through stellar encounters in GCs is less dominant than previously suggested, and that the primordial formation channel has a substantial contribution. Taking these aspects together, we suggest that a large fraction of primordial, soft binaries have been disrupted in binary–single or binary–binary stellar interactions before they could otherwise evolve into X-ray-emitting close binaries, whereas the same interactions also have led to the formation of new close binaries. No significant correlations between and cluster properties, including dynamical age, metallicity, and structural parameters, are found.

X-RAY EMISSIVITY OF OLD STELLAR POPULATIONS: A LOCAL GROUP CENSUS

We study the unresolved X-ray emission in three Local Group dwarf elliptical galaxies (NGC 147, NGC 185 and NGC 205) using XMM-Newton observations, which most likely originates from a collection of weak X-ray sources, mainly cataclysmic variables and coronally active binaries. Precise knowledge of this stellar X-ray emission is crucial not only for understanding the relevant stellar astrophysics but also for disentangling and quantifying the thermal emission from diffuse hot gas in nearby galaxies.We find that the integrated X-ray emissivities of the individual dwarf ellipticals agree well with that of the Solar vicinity, supporting an often assumed but untested view that the X-ray emissivity of old stellar populations is quasi-universal in normal galactic environments, in which dynamical effects on the formation and destruction of binary systems are not important. The average X-ray emissivity of the dwarf ellipticals, including M32 studied in the literature, is measured to be $L_{0.5-2\ \rm {keV}}/M_{\ast} = (6.0 \pm 0.5 \pm 1.8) \times 10^{27} \ \rm{erg \ s^{-1} \ M_\odot^{-1}}$. We also compare this value to the integrated X-ray emissivities of Galactic globular clusters and old open clusters and discuss the role of dynamical effects in these dense stellar systems.

A Spitzer Space Telescope survey of extreme asymptotic giant branch stars in M32

We investigate the population of cool, evolved stars in the Local Group dwarf elliptical galaxy M32, using Infrared Array Camera observations from the Spitzer Space Telescope. We construct deep mid-infrared colour-magnitude diagrams for the resolved stellar populations within 3.5 arcmin of M32's centre, and identify those stars that exhibit infrared excess. Our data is dominated by a population of luminous, dust-producing stars on the asymptotic giant branch (AGB) and extend to approximately 3 mag below the AGB tip. We detect for the first time a sizeable population of `extreme' AGB stars, highly enshrouded by circumstellar dust and likely completely obscured at optical wavelengths. The total dust-injection rate from the extreme AGB candidates is measured to be $7.5 \times 10^{-7}$ ${\rm M}_{\odot} \, {\rm yr}^{-1}$, corresponding to a gas mass-loss rate of $1.5 \times 10^{-4}$ ${\rm M}_{\odot} \, {\rm yr}^{-1}$. These extreme stars may be indicative of an extended star-formation epoch between 0.2 and 5 Gyr ago.

The ancient stellar population of M 32: RR Lyrae variable stars confirmed

Using archival multi--epoch ACS/WFC images in the F606W and F814W filters of a resolved stellar field in Local Group dwarf elliptical galaxy M32 we have made an accurate Colour-Magnitude Diagram and a careful search for RR Lyr variable stars. We identified 416 bona fide RR Lyr stars over our field of view, and their spatial distribution shows a rising number density towards the centre of M32. These new observations clearly confirm the tentative result of Fiorentino et al. (2010), on a much smaller field of view, associating an ancient population of RR Lyr variables to M32. We associate at least 83 RR Lyr stars in our field to M32. In addition the detection of 4 Anomalous Cepheids with masses in the range 1.2-1.9 Mo indicates the presence of relatively young, 1-4 Gyr old, stars in this field. They are most likely associated to the presence of the blue plume in the Colour-Magnitude Diagram. However these young stars are unlikely to be associated with M32 because the radial distribution of the blue plume does not follow the M32 density profile, and thus they are more likely to belong to the underlying M31 stellar population. Finally the detection of 3 Population II Cepheids in this field gives an independent measurement of the distance modulus in good agreement with that obtained from the RRLyr, mu0=24.33 +- 0.21 mag.

The internal dynamics of the Local Group dwarf elliptical galaxies NGC 147, 185 and 205

We present three-integral dynamical models for the three Local Group dwarf elliptical galaxies: NGC 147, 185 and 205. These models are fitted to the Two-Micron All-Sky Survey (2MASS) J-band surface-brightness distribution and the major-axis kinematics (mean streaming velocity and velocity dispersion) and, in the case of NGC 205, also to the minor-axis kinematics. The kinematical information extends out to 2R e in the case of NGC 205 and out to about 1R e in the case of NGC 147 and 185. It is the first time models are constructed for the Local Group dwarf ellipticals (dEs) that allow for the presence of dark matter at large radii and that are constrained by kinematics out to at least one half-light radius. The B-band mass-to-light ratios of all the three galaxies are rather similar, (M/L) B ≈ 3-4 M ⊙ /L ⊙,B . Within the inner two half-light radii, about 40-50 per cent of the mass is in the form of dark matter, so dEs contain about as much dark matter as bright ellipticals. Based on their appreciable apparent flattening, we modelled NGC 205 and 147 as being viewed edge-on. For NGC 185, having a much rounder appearance on the sky, we produced models for different inclinations. NGC 205 and 147 have a relatively isotropic velocity dispersion tensor within the region where the internal dynamics are strongly constrained by the data. Our estimated inclination for NGC 185 is i ≈ 50° because in that case the model has an intrinsic flattening close to the peak of the intrinsic shape distribution of dEs and it, like the best-fitting models for NGC 147 and 205, is nearly isotropic. We also show that the dynamical properties of the bright nucleus of NGC 205 are not unlike those of a massive globular cluster.

Local Group Dwarf Galaxies and the Fundamental Manifold of Spheroids

The fundamental manifold (FM), an extension of the fundamental plane formalism, incorporates all spheroid-dominated stellar systems from dwarf ellipticals up to the intracluster stellar populations of galaxy clusters by accounting for the continuous variation of the mass-to-light ratio within the effective radius r_e with scale. Here, we find that Local Group dwarf spheroidal and dwarf elliptical galaxies, which probe the FM relationship roughly one decade lower in r_e than previous work, lie on the extrapolation of the FM. When combined with the earlier data, these Local Group dwarfs demonstrate the validity of the empirical manifold over nearly four orders of magnitude in r_e. The continuity of the galaxy locus on the manifold and, more specifically, the overlap on the FM of dwarf ellipticals like M 32 and dwarf spheroidals like Leo II, implies that dwarf spheroidals belong to the same family of spheroids as their more massive counterparts. The only significant outliers are Ursa Minor and Draco. We explore whether the deviation of these two galaxies from the manifold reflects a breakdown in the coherence of the empirical relationship at low luminosities or rather the individual dynamical peculiarities of these two objects. We discuss some implications of our results for how the lowest mass galaxies form.

Local Group Dwarf Elliptical Galaxies. I. Mapping the Dynamics of NGC 205 Beyond the Tidal Radius

NGC 205 is the nearest example of a dwarf elliptical galaxy and the prototype of this enigmatic galaxy class. Photometric evidence suggests that NGC 205, a close satellite of the M31 galaxy, is tidally interacting with its parent galaxy. We present stellar radial velocity measurements out to a projected radius of 20' (5 kpc) in NGC 205 based on Keck DEIMOS multislit spectroscopic observations of 725 individual red giant branch stars. Our kinematic measurements extend from the center out to 6 times the effective radius of NGC 205, well past the expected tidal radius. The contamination in our kinematic sample from M31 field stars is estimated to be a few percent based on maximum likelihood fits to the distribution of stars in position-velocity space. We measure a maximum major-axis rotation speed for the body of NGC 205 of 11 ± 5 km s-1 and note that this is based on observing a definite turnover in the rotation curve; this is the first dE galaxy in which the maximum rotation velocity has been measured. Combined with the velocity dispersion, we conclude that NGC 205 is supported by a combination of rotation and anisotropic velocity dispersion. At a major-axis distance of 45 (1 kpc), the velocity profile of NGC 205 turns over; stars beyond this radius are moving counter to the rotation of the inner part of the galaxy. The turnover radius is coincident with the onset of isophotal twisting and the estimated tidal radius, suggesting that the outer kinematics of NGC 205 is dominated by gravitational interactions with the nearby M31 galaxy. The motion of stars beyond a radius of ~45 implies that NGC 205 is in a prograde encounter with its parent galaxy, M31.

The Asymptotic Giant Branch of NGC 205: The Characteristics of Carbon Stars and M Giants Identified fromJHK′ Images

J, H, and K' images are used to investigate the asymptotic giant branch (AGB) content of the Local Group dwarf elliptical galaxy NGC 205. The AGB on the (K, H-K) and (K, J-K) color-magnitude diagrams consists of two sequences: a near-vertical plume of giants with spectral types K and M and a red arm containing C stars. There are 320 C stars with Mbol 1.5 within 2' of the nucleus. C stars account for 10% of the integrated luminosity of AGB stars brighter than Mbol = -3.75 near the center of NGC 205, and this is in excellent agreement with what is measured in intermediate-age clusters in the LMC. The most luminous AGB star has Mbol = -6.5, although variability introduces an uncertainty of a few tenths of a magnitude when using this as an estimate of the AGB tip brightness. Comparisons with models suggest that the brightest AGB stars formed within the past 0.1 Gyr and that the previous episode of star formation occurred a few tenths of a Gyr earlier. These results are consistent with star formation in NGC 205 being triggered by interactions with M31. These data also demonstrate that near-infrared imaging provides an efficient means of identifying C stars in nearby galaxies. The techniques used here to identify C stars and probe the AGB are well suited to studies of galaxies outside of the Local Group using data obtained with adaptive optics systems on large ground-based telescopes.

The Star Formation History of the Local Group Dwarf Elliptical Galaxy NGC 185. II. Gradients in the Stellar Population

The star formation history of the dE NGC 185, together with its spatial variations, has been investigated using new ground-based $H_\alpha$ and $BVI$ photometry, and synthetic color--magnitude diagrams (CMDs). We find that the bulk of the stars were formed in NGC 185 at an early epoch of its evolution. After that, the star formation proceeded at a low rate until the recent past, the age of the most recent traces of star formation activity detected in the galaxy being some 100 Myr. The star formation rate, $\psi(t)$ for old and intermediate ages shows a gradient in the sense of taking smaller values for higher galactocentric radii. Moreover, recent star formation is detected in the central $150 \times 90$ pc$^2$ only, where the youngest, 100 Myr old population is found. The luminous blue {\it stars} discovered by Baade (1951) in the center of NGC 185 are discussed using new CCD images in $B$ and Baade's original photographic plates, reaching the conclusion that most of them are in fact star clusters. A consistent picture arises in which the gas observed in the central region of NGC 185 would have an internal origin. The rate at which evolved stars return gas to the ISM is enough to seed the recent star formation observed in the center of the galaxy and the SN rate is probably low enough to allow the galaxy to retain the gas not used in the new stellar generations.

Properties of Two New M31 Dwarf Spheroidal Companions from Keck Imaging

We have obtained images in V and I of the newly discovered Local Group dwarf galaxies Pegasus dSph and Cassiopeia dSph and their surrounding field using the Keck 10 m telescope and Low-Resolution Imaging Spectrograph. The first stellar luminosity functions and color-magnitude diagrams are presented for stars with V25 and I24. The distances to the new dwarfs are estimated from the apparent I magnitude of the tip of the red giant branch to be DMW(Peg dSph) = 830?80 kpc and DMW(Cas dSph) = 760?70 kpc, which are consistent with their belonging to the extended M31 satellite system. Both galaxies are dwarf spheroidals (dSph's) with red giant branch morphologies indicating predominantly old stellar populations and estimated mean metallicities, [Fe/H], of -1.3?0.3 for Peg dSph and -1.4?0.3 for Cas dSph. Their central surface brightness-[Fe/H]-absolute magnitude relationship follows that of other Local Group dSph, dwarf elliptical, and dwarf irregular galaxies. In contrast to four out of nine Milky Way dSph's (the four that lie beyond D=100 kpc), none of the six known M31 dSph's appear to have a dominant intermediate-age population.

The Star Formation History of the Local Group Dwarf Elliptical Galaxy NGC 185. I. Stellar Content

?????We present VI CCD photometry of ~16,000 stars in a 72 ? 72 field of the Local Group dwarf elliptical galaxy NGC 185. The resulting VI color-magnitude diagram reveals a dominant red giant branch population, an important number of luminous red stars located above the tip of the red giant branch, and a number of blue and yellow stars. Besides the nucleus, our field also covers a large, less crowded area of the galaxy. We show color-magnitude diagrams at six different distances from the nucleus. The red giant branch becomes substantially narrower at larger distances from the nucleus, while the photometry gets deeper. In this paper, we concentrate on investigating the contribution of the observational effects (mainly crowding) to this observed gradient. Although we cannot rule out here the possibility that this trend partially originates in a gradient of the characteristics of the stellar populations of the galaxy with radius, we show that a strong radial gradient exists in the observational effects that can mimic a gradient in the real properties (e.g., age, metallicity) of the stellar population. A distance modulus of m - M = 23.95 ? 0.10 has been obtained from the tip of the red giant branch, in good agreement with previous estimates. The average stellar metallicity is estimated to be [Fe/H] = -1.43 ? 0.15, and decreases for increasing galactocentric distance.

Dwarf Elliptical Galaxies in the M81 Group: The Structure and Stellar Populations of BK5N and F8D1

The M81 group is one of the nearest groups of galaxies, but its properties are quite different from those of the Local Group. It has therefore provided a different environment for the evolution of its member galaxies. We have carried out a CCD survey of the M81 group to search for analogs to Local Group dwarf elliptical (dE) galaxies. All the M81 dwarfs previously identified in photographic surveys were recovered and we also discovered several new systems whose surface brightnesses fall within the range found for Local Group dE’s.We have obtained HST WFPC2 images through the F555W and F814W filters of two M81 group dE’s: BK5N and a new system, designated F8D1. The resulting color-magnitude diagrams show the upper two magnitudes of the red giant branch. The I magnitudes of the red giant branch tip in both galaxies yield distances that are consistent with membership in the M81 group. Surface brightness and total magnitude measurements indicate that BK5N and F8D1 have similar central surface brightness (24.5 and 25.4 mag arcsec-2 in V, respectively), but F8D1 is larger length scale results in it being 3 magnitudes more luminous than BK5N. BK5N lies on the relation between central surface brightness and absolute magnitude defined by Local Group dwarf ellipticals, but F8D1 does not. F8D1 is more luminous for its central surface brightness than the relation predicts, similar to the large low surface brightness dwarf galaxies found in, for example, Virgo. The mean color of the giant branch is used to establish the mean abundance of each galaxy. F8D1, the more luminous galaxy, is significantly more metal rich ([Fe/H] ≈ -1.0) than BK5N ([Fe/H] ≈ -1.7). Both BK5N and F8D1 lie on the relation between absolute magnitude and metal abundance defined by Local Group dwarf ellipticals. However, as regards the relation between central surface brightness and metal abundance, BK5N again follows the Local Group dwarfs, while F8D1 deviates significantly from this relation. This suggests that the total amount of luminous matter is more fundamental in controlling metal enrichment than the surface density of luminous matter. We have also used the color width of the giant branch compared with the photometric errors to establish abundance ranges in both galaxies, the sizes of which are comparable to those in Local Group dE’s.

Luminous Red Stars in Local Group Dwarf Elliptical Galaxies: An Intermediate-Age Population?

In this paper, we show that the optically bright stars above the tip of the first red giant branch (TRGB) in the color magnitude (CM) diagrams of nearby dwarf elliptical (dE) galaxies, commonly interpreted as indication of the existence of an intermediate-age population, may, in certain circumstances, be an artifact of observational effects on a pure old population system. For this purpose, model CM diagrams have been computed simulating the observational effects that can be found in different regions of a Local Group dE galaxy. The starting synthetic CM diagram represents a pure old system, with star formation extending only from 15 to 12 Gyr ago. Based on those model diagrams, we analyze the conclusions that a hypothetical ground-based observer might reach concerning the presence of a population of stars above the tip of the red giant branch (TRGB) that could be interpreted as an intermediate-age population, by using two age indicators extensively employed in the literature: i) the bolometric magnitude at the tip of the asymptotic giant branch (AGB) phase, and ii) the ratio of AGB to red giant branch (RGB) stars present in the CM diagram. Our analysis shows that, if observational effects are overlooked, application of both methods would result in finding a fictitious intermediate-age population in the inner regions of the galaxy, where crowding is more severe.

Stellar Populations in the Dwarf Elliptical Galaxy NGC 147

Deep V and I CCD images in a central and an outer field of the Local Group dwarf elliptical galaxy NGC 147 have been obtained with the Wide Field and Planetary Camera-2 (WFPC2) on board of the Hubble Space Telescope. The color-magnitude diagram shows a number of interesting features, including a well defined red giant branch (RGB), a red horizontal branch (HB), a strong red clump, and a small number of extended asymptotic giant branch (EAGB) stars. A mean distance modulus of (m- M)_0=24.39 is derived based on both the HB and the RGB tip brightness. The metallicity [Fe/H] as determined from the RGB color has a mean value of -0.91 in the central field, and -1.0 in the outer field; and the outer field shows a weak tendency of increasing metallicity with galactocentric radius. A metallicity dispersion is also present in the galaxy, and it shows a clear radial variation in the sense that a larger dispersion is seen at smaller radii. The small population of EAGB stars indicates the presence of intermediate-aged (several Gyr) stars in the galaxy, while the absence of the main sequence stars with M v< 1 shows that star formation ceased at least 1 Gyr ago. The distribution of the EAGB stars indicates that the younger stars are more centrally concentrated than the majority of older stars. A similar age gradient is also implied by the relative distribution of the HB stars, which appear to be more populous at larger radii. These results are considered within the context of theoretical models for the evolution of dwarf elliptical galaxies.

HI Observations of the Tucana Dwarf Elliptical Galaxy

view Abstract Citations (40) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS HI Observations of the Tucana Dwarf Elliptical Galaxy Oosterloo, T. ; Da Costa, G. S. ; Staveley-Smith, L. Abstract H I observations of the Local Group dwarf elliptical galaxy, Tucana, have been obtained with the Australia Telescope Compact Array. Within the optical extent of this galaxy, no H I was detected. The upper limit on the H I mass to blue luminosity ratio, M_HI_/L_B_ , is then ~10^-2^ for Tucana, a value similar to those of the Galactic dwarf spheroidal companions. This nondetection contrasts with the modest H I contents of Phoenix and LGS3, the other relatively isolated Local Group dwarfs with dominant old stellar populations. However, an H I cloud was detected, some 15' to the north-east of Tucana, at a heliocentric velocity of 130+/-2 km s^-1^. CCD observations of the central regions of this cloud, which has a maximum extent of ~20' x 10', did not reveal any obvious optical counterpart. The cloud has a faint tail of emission that points in the general direction of Tucana, and if it is at the same distance as the dE galaxy, then the H I mass is ~1.5 x 10^6^ M_sun_. We prefer the alternative interpretation that this H I cloud is a foreground high- velocity cloud, probably associated with the Magellanic Stream complex that pervades this part of the southern sky. Publication: The Astronomical Journal Pub Date: November 1996 DOI: 10.1086/118155 Bibcode: 1996AJ....112.1969O Keywords: GALAXIES: INDIVIDUAL: TUCANA; GALAXIES: ABUNDANCES; GALAXIES: PECULIAR; GALAXIES: ELLIPTICAL AND LENTICULAR full text sources ADS | data products SIMBAD (10) NED (1)

V and I photometry of bright giants in the central regions of NGC 147

view Abstract Citations (26) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS V and I Photometry of Bright Giants in the Central Regions of NGC 147 Davidge, T. J. Abstract Deep V and I CCD images with subarcsec spatial resolution are used to investigate the stellar content of the central regions of the Local Group dwarf elliptical galaxy NGC 147. Red giant branch (RGB) stars are resolved over the entire field, and the RGB-tip occurs at I ~ 20.5, suggesting that the distance modulus is 24.3. A comparison_with globular cluster sequences indicates that the center of NGC 147 is moderately metal-poor, with [Fe/H]^bar^ ~ -1. This is not significantly different from what was found in the outer regions of the galaxy by Mould et al. (ApJ, 270,471(1983)]. Moreover, the width of the V - I color distribution at I = 21.0 indicates that a spread in metallicity is present, with σ_[Fe/H]_ ~ +/-0.3. There is no evidence of a component more metal- poor than [Fe/H]~ -1.3. A small population of moderately bright asymptotic giant branch (AGB) stars has also been detected, and the AGB- tip occurs near M_bol_ ~ -5.0, indicating that an intermediate-age population is present. It is estimated that the intermediate-age population contributes ~2%-3% of the V light from NGC 147. Publication: The Astronomical Journal Pub Date: December 1994 DOI: 10.1086/117224 arXiv: arXiv:astro-ph/9410042 Bibcode: 1994AJ....108.2123D Keywords: Asymptotic Giant Branch Stars; Dwarf Galaxies; Elliptical Galaxies; Globular Clusters; Hydrogen; Iron; Metallicity; Red Giant Stars; Andromeda Galaxy; Astronomical Photometry; Brightness; Charge Coupled Devices; Local Group (Astronomy); Stellar Color; Stellar Luminosity; Astronomy; GALAXIES: STELLAR CONTENT; GALAXIES: INDIVIDUAL: NGC 147; Astrophysics E-Print: 18 pages LaTeX, 7 figures upon request, SISSA-DAO-94-006 full text sources arXiv | ADS | data products SIMBAD (7) NED (3)

The distribution and age of asymptotic giant branch stars in NGC 205

V and I CCD images are used to investigate the spatial distribution and age of bright asymptotic giant branch (AGB) stars in the central regions of the Local Group dwarf elliptical galaxy NGC 205. These data reveal a large intermediate-age component, which is uniformly distributed over the central regions of the galaxy. The redward extent of the bright AGB sequence on the (I, V-I) diagram suggests that the majority of these objects have metallicities which are roughly solar

Stellar content of nearby galaxies. II - The Local Group dwarf elliptical galaxy M32

view Abstract Citations (99) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar Content of Nearby Galaxies. II. The Local Group Dwarf Elliptical Galaxy M32 Freedman, Wendy L. Abstract A field in the elliptical galaxy M32 has been resolved into stars using the prime-focus CCD camera on the Canada-France-Hawaii telescope. From these observations color-magnitude diagrams have been obtained for the brightest stars in this high-surface-brightness companion galaxy to M31. Both the I vs (V - I) and I vs (R - I) CCD color-magnitude diagrams reveal a red population of stars, the brightest of which resolve at I~19.5 mag. A lower limit to the mean metallicity of this stellar population is estimated from the apparent mean (V - I) and (R - I) colors at the giant branch tip. For the available data, this method indicates that the mean metallicity is greater than that of the most metal-rich Galactic globular clusters, that is (M/H) > -0.5 dex. The dispersion in the (V - I) and (R - I) colors exceeds that due to the estimated photometric errors, probably indicating an intrinsic range in the metallicity of the population amounting to 0.6 dex. The observed numbers of stars bracketing the tip of the first red giant branch can, in principle, provide a constraint on the age of the observed population. The histogram Iband luminosity function shows two discontinuities and allows two possible interpretations. If the bright discontinuity seen at I = 20.15 +/- 0.10 mag is interpreted as the tip of the first red giant branch, it suggests that M32 is approximately 100 kpc closer than M31, and that the age of most of the M32 stars is comparable to those in Galactic globular clusters. This result is consistent with other determinations of the relative distances of M31 and M32. Alternatively, if the fainter discontinuity at I = 20.45 +/- 0.10 mag is interpreted as being the first red giant branch tip, this suggests that M32 is at a distance comparable to M31. In this case, the relative numbers of stars above and below the adopted red giant branch tip suggests that a significant population of asymptotic giant branch stars may be present which could have formed as recently as 5 Gyr ago. This interpretation is consistent with spectroscopic studies and population synthesis models of the nucleus of M32. An independent distance modulus estimate for M32 is needed to provide a means of discriminating between these two very different alternatives. Publication: The Astronomical Journal Pub Date: October 1989 DOI: 10.1086/115216 Bibcode: 1989AJ.....98.1285F Keywords: Color-Magnitude Diagram; Dwarf Galaxies; Elliptical Galaxies; Local Group (Astronomy); Stellar Spectrophotometry; Astronomical Catalogs; Background Radiation; Charge Coupled Devices; Stellar Luminosity; Astrophysics; GALAXIES: INDIVIDUAL; GALAXIES: LOCAL GROUP; GALAXIES: STELLAR CONTENT full text sources ADS | data products SIMBAD (5) NED (1) Related Materials (2) Part 1: 1988AJ.....96.1248F Part 3: 1990AJ.....99..149W

A search for RR Lyrae variables in NGC 147

view Abstract Citations (13) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Search for RR Lyrae Variables in NGC 147 Saha, A. ; Hoessel, J. G. Abstract Repeated deep CCD observations of a field in the Local Group dwarf elliptical galaxy NGC 147 have been compared, and 34 variable stars have been found. Light curves of 13 of these have been obtained. Periods and shapes indicate that nine of these 13 are RR Lyrae stars. The intensity-averaged phase-weighted-mean g magnitude is 25.15 (+0.17 or -0.15), which implies, after correction for extinction, that the distance modulus to NGC 147 is 23.85 (+0.22 or -0.20), or 589 kpc, as compared to Pritchet and van den Bergh's (1987) distance of 738 kpc for M31. Publication: The Astronomical Journal Pub Date: December 1987 DOI: 10.1086/114587 Bibcode: 1987AJ.....94.1556S Keywords: Dwarf Galaxies; Elliptical Galaxies; Local Group (Astronomy); Spectrum Analysis; Stellar Spectrophotometry; Variable Stars; Charge Coupled Devices; Interstellar Extinction; Light Curve; Stellar Magnitude; Astrophysics; GALAXIES: GENERAL; STARS: PULSATION full text sources ADS | data products SIMBAD (16) NED (15)