Main-sequence Luminosity Research Articles

New Determination of Fundamental Properties of Palomar 5 Using Deep DESI Imaging Data

Abstract The legacy imaging surveys for the Dark Energy Spectroscopic Instrument project provides multiple-color photometric data, which are about 2 mag deeper than those from the SDSS. In this study, we redetermine the fundamental properties for an old halo globular cluster of Palomar 5 based on these new imaging data, including structure parameters, stellar population parameters, and luminosity and mass functions. These characteristics, together with its tidal tails, are key for dynamical studies of the cluster and constraining the mass model of the Milky Way. By fitting the King model to the radial surface density profile of Palomar 5, we derive the core radius of , tidal radius of , and concentration parameter of c = 0.78 ± 0.04. We apply a Bayesian analysis method to derive the stellar population properties and get an age of 11.508 ± 0.027 Gyr, metallicity of [Fe/H] = −1.798 ± 0.014, reddening of E(B − V) = 0.0552 ± 0.0005, and distance modulus of . The main-sequence luminosity and mass functions for both the cluster center and tidal tails are investigated. The luminosity and mass functions at different distances from the cluster center suggest that there is obvious spatial mass segregation. Many faint low-mass stars have been evaporated at the cluster center, and the tidal tails are enhanced by low-mass stars. Both the concentration and relaxation times suggest that Palomar 5 is a totally relaxed system.

The initial mass function in the extended ultraviolet disc of M83

ABSTRACT Using Hubble Space Telescope ACS/WFC data we present the photometry and spatial distribution of resolved stellar populations of four fields within the extended ultraviolet disc (XUV disc) of M83. These observations show a clumpy distribution of main-sequence stars and a mostly smooth distribution of red giant branch stars. We constrain the upper end of the initial mass function (IMF) in the outer disc using the detected population of main-sequence stars and an assumed constant star formation rate (SFR) over the last 300 Myr. By comparing the observed main-sequence luminosity function to simulations, we determine the best-fitting IMF to have a power-law slope α = −2.35 ± 0.3 and an upper mass limit $M_{\rm u}=25_{-3}^{+17} \, \mathrm{M}_\odot$. This IMF is consistent with the observed H $\rm \alpha$ emission, which we use to provide additional constraints on the IMF. We explore the influence of deviations from the constant SFR assumption, finding that our IMF conclusions are robust against all but strong recent variations in SFR, but these are excluded by causality arguments. These results, along with our similar studies of other nearby galaxies, indicate that some XUV discs are deficient in high-mass stars compared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc, many already observed with HST, thus allowing a more comprehensive investigation of the IMF, and how it varies, using the techniques developed here.

The Binary Dwarf Carbon Star SDSS J125017.90+252427.6

Abstract Although dwarf carbon (dC) stars are universally thought to be binaries in order to explain the presence of C 2 in their spectra while still near main-sequence luminosity, direct observational evidence for their binarity is remarkably scarce. Here, we report the detection of a 2.92 day periodicity in both the photometry and radial velocity of SDSS J125017.90+252427.6, an r = 16.4 dC star. This is the first photometric binary dC, and only the second dC spectroscopic binary. The relative phase of the photometric period to the spectroscopic observations suggests that the photometric variations are a reflection effect due to heating from an unseen companion. The observed radial velocity amplitude of the dC component (K = 98.8 ± 10.7 km s−1) is consistent with a white dwarf companion, presumably the evolved star that earlier donated the carbon to the dC, although substantial orbital evolution must have occurred. Large synoptic photometric surveys such as the Palomar Transient Factory, which was used for this work, may prove useful for identifying binaries among the shorter-period dC stars.

Light curve analysis of a new W UMa system GSC 3581-1856

New BVRI photometric observations covering seven minima times for the eclipsing binary GSC 3581-1856 were presented. The light curves in BVRI colours were analysed by using PHOEBE code for the system parameters. New minima times were used in revising the light elements. The system is found a W-type contact binary with mass ratio of q = 1.3362 ± 0.0042 and a fill out parameter of f = 16.89 ± 3.17% . The smaller and less massive component was found hotter component (T1 ≃ 5590 K). Lower temperature (T2 = 5295 K) of the mass accreting more massive component is probably due to a disk or envelope around this star. The original temperature of the more massive secondary component would be at least T2 ≃ 5590 K. The preliminary absolute dimensions (M1 = 0.78 ± 0.01 M⊙, M2 = 1.05 ± 0.01 M⊙, R1 = 0.92 ± 0.10 R⊙, R2 = 1.05 ± 0.20 R⊙, L1 =0.86 ± 0.20 L⊙ and L2 = 1.00 ± 0.20 L⊙) indicate a relatively young marginal contact binary for GSC 3581-1856 system. The present luminosity of the less massive but hotter component would be not much different from its main sequence luminosity, and thus its original mass was estimated to be slightly more than one solar mass. This means it could be transferred and/or lost about 30% of its original mass which place the system in relatively young system in contact phase.

First photometric study of the W UMa system GSC 1042-2191

We present new photometric observations covering eight minima times for the eclipsing binary GSC 1042-2191. The light curves in BVRI colors were analyzed by using WD-code for the system parameters. Eight minima times were obtained from the new observations. The system is found a low mass ratio (q = 0.148), A-type over-contact binary with a fill out parameter of f = 65.01 ± 12.18%. The preliminary absolute dimensions (M1= 1.26 ± 0.06 M⊙, M2 = 0.18 ± 0.06 M⊙, R1 = 1.54 ± 0.20 R⊙, R2 = 0.69 ± 0.01 R⊙, L1 =3.30 ± 0.30 L⊙ and L2 = 0.59 ± 0.20 L⊙) indicate the very much oversized and over-luminous secondary component, by assuming the present luminosity of the secondary is its main sequence luminosity, we predict the original mass is about 0.8 M⊙, this means the present secondary could be transferred and/or lost 77% of its original mass and only its core is left.

FS CMa Type Binaries

FS CMa type stars is a group of ~70 objects formerly known as unclassified stars with the B[e] phenomenon. Their very strong emission-line spectra in combination with a nearly main-sequence luminosity suggest the binary nature for them. They possess strong IR excesses due to radiation of circumstellar dust that implies a compact distribution probably in a circumbinary disk. Our long-term spectroscopic monitoring revealed neutral metal lines, which always include that of Li I 6708 \AA, in the spectra of some FS CMa objects indicating the presence of a cool star. We present a summary of our results with a first overview of FS CMa type binaries and review possible implications for the nature and evolutionary status of the entire group.

The initial mass function and star formation law in the outer disc of NGC 2915

Using Hubble Space Telescope (HST) Advanced Camera for Surveys/Wide Field Camera data we present the photometry and spatial distribution of resolved stellar populations in the outskirts of NGC 2915, a blue compact dwarf with an extended H i disc. These observations reveal an elliptical distribution of red giant branch stars, and a clumpy distribution of main-sequence stars that correlate with the H i gas distribution. We constrain the upper-end initial mass function (IMF) and determine the star formation law (SFL) in this field, using the observed main-sequence stars and an assumed constant star formation rate. Previously published Hα observations of the field, which show one faint H ii region, are used to provide further constraints on the IMF. We find that the main-sequence luminosity function analysis alone results in a best-fitting IMF with a power-law slope α = −2.85 and upper-mass limit |$\rm M_u = 60\,\mathrm{M}_{\odot }$|⁠. However, if we assume that all Hα emission is confined to H ii regions then the upper-mass limit is restricted to |$\rm M_u \lesssim 20\, \mathrm{M}_{\odot }$|⁠. For the luminosity function fit to be correct, we have to discount the Hα observations implying significant diffuse ionized gas or escaping ionizing photons. Combining the HST photometry with H i imaging, we find the SFL has a power-law index N = 1.53 ± 0.21. Applying these results to the entire outer H i disc indicates that it contributes 11–28 per cent of the total recent star formation in NGC 2915, depending on whether the IMF is constant within the disc or varies from the centre to the outer region.

PHOTOMETRIC AND STRUCTURAL PROPERTIES OF NGC 6544: A COMBINED VVV-HUBBLE SPACE TELESCOPESTUDY

We combine archival Hubble Space Telescope imaging with wide-field near-infrared photometry to study the neglected metal-poor Galactic globular cluster NGC 6544. A high spatial resolution map of differential reddening over the inner portion of the cluster is constructed, revealing variations of up to half of the total reddening, and the resulting corrected color-magnitude diagrams reveal a sparse blue horizontal branch and centrally concentrated blue straggler population, verified via relative proper motions. Using the corrected photometry to investigate the cluster distance, reddening, and age via direct comparison to well-calibrated photometry of clusters with similar metallicities, we estimate (m – M)0 = 11.96, E(B – V) = 0.79, and an age coeval with M13 to within the relevant uncertainties. Although our data are insufficient to place tight constraints on the reddening law toward NGC 6544, we find no strong evidence that it is non-standard at optical or near-infrared wavelengths. We also provide near-infrared fiducial sequences extending nearly 2 mag below the cluster main sequence turnoff, generated from a statistically decontaminated sample of cluster stars. Lastly, we redetermine the cluster center and construct a radial number density profile which is well fit by an atypically flat power law with a slope of about 1.7. We discuss this result, together with a flattened main sequence luminosity function and inverted mass function, in the context of mass segregation and tidal stripping via interactions with Milky Way potential.

TOWARD UNDERSTANDING THE B[e] PHENOMENON. IV. MODELING OF IRAS 00470+6429

FS CMa type stars are a recently described group of objects with the B[e] phenomenon that exhibit strong emission-line spectra and strong IR excesses. In this paper we report the first attempt for a detailed modeling of IRAS 00470+6429, for which we have the best set of observations. Our modeling is based on two key assumptions: the star has a main-sequence luminosity for its spectral type (B2) and the circumstellar envelope is bimodal, composed of a slowly outflowing disk-like wind and a fast polar wind. Both outflows are assumed to be purely radial. We adopt a novel approach to describe the dust formation site in the wind that employs timescale arguments for grain condensation and a self-consistent solution for the dust destruction surface. With the above assumptions we were able to reproduce satisfactorily many observational properties of IRAS 00470+6429, including the H line profiles and the overall shape of the spectral energy distribution. Our adopted recipe for dust formation proved successful in reproducing the correct amount of dust formed in the circumstellar envelope. Possible shortcomings of our model, as well as suggestions for future improvements, are discussed.

The circumstellar environment of the FS CMa star IRAS 00470+6429

AbstractFS CMa type stars are a recently described group of objects with the B[e] phenomenon that exhibit strong emission-line spectra and strong IR excesses. In this paper we report the first attempt for a detailed modeling of IRAS 00470+6429, for which we have the best set of observations. Our modeling is based on two key assumptions: the star has a main-sequence luminosity for its spectral type (B2) and that the circumstellar (CS) envelope is bimodal, composed of a slowly outflowing disk-like wind and a fast polar wind. Both outflows are assumed to be purely radial. We adopt a novel approach to describe the dust formation site in the wind that employs timescale arguments for grain condensation and a self-consistent solution for the dust destruction surface. With the above assumptions we were able to reproduce satisfactorily many observational properties of IRAS 00470+6429, including the HI line profiles and the overall shape of the spectral energy distribution.

The Intermediate-Age Globular Cluster NGC 1783 in the Large Magellanic Cloud

We present Hubble Space Telescope ACS deep photometry of the intermediate-age globular cluster NGC 1783 in the Large Magellanic Cloud. By using this photometric data set, we have determined the degree of ellipticity of the cluster ( = 0.14 ± 0.03) and the radial density profile. This profile is well reproduced by a standard King model with an extended core (rc = 24.5'') and a low concentration (c = 1.16), indicating that the cluster has not experienced the collapse of the core. We also derived the cluster age using the Pisa Evolutionary Library isochrones, with three different amounts of overshooting (namely, Λos = 0.0, 0.10, and 0.25). From a comparison of the observed color-magnitude diagram and main-sequence luminosity function (LF) with the theoretical isochrones and LFs, we find that only models with the inclusion of some overshooting (Λos = 0.10-0.25) are able to reproduce the observables. By using the magnitude difference δV = 0.90 between the mean level of the He clump and the flat region of the SGB, we derive an age τ = 1.4 ± 0.2 Gyr.

The Low‐Mass Initial Mass Function of the Field Population in the Large Magellanic Cloud withHubble Space TelescopeWFPC2 Observations

We present V- and I-equivalent HST WFPC2 stellar photometry of an area in the Large Magellanic Cloud (LMC), located to the west of the bar of the galaxy, which accounts for the general background field of its inner disk. The WFPC2 observations reach magnitudes as faint as V = 25 mag, and the large sample of more than 80,000 stars allows us to determine in detail the present-day mass function (PDMF) of the detected main-sequence stars, which is identical to the initial mass function (IMF) for masses M 1 M☉. The low-mass main-sequence mass function of the LMC field is found not to have a uniform slope throughout the observed mass range; i.e., the slope does not follow a single power law. This slope changes at about 1 M☉ to become more shallow for stars with smaller masses down to the lowest observed mass of ~0.7 M☉, giving clear indications of flattening for even smaller masses. We verified statistically that for stars with M 1 M☉ the IMF has a slope Γ around -2, with an indicative slope Γ -1.4 for 0.7 M/M☉ 0.9, while for more massive stars the main-sequence mass function becomes much steeper with Γ -5. The main-sequence luminosity function (LF) of the observed field is in very good agreement with the Galactic LF as it was previously found. Taking into account several assumptions concerning evolutionary effects, which should have changed through time the stellar content of the observed field, we reconstruct qualitatively its IMF for the whole observed mass range (0.7 M/M☉ 2.3), and we find that the number of observed evolved stars is not large enough to have affected significantly the form of the IMF, which thus is found almost identical to the observed PDMF.

Photometric study of the eclipsing binary V1034 Sco

We present multi-colour Stromgren photometry of the eclipsing binary V1034 Sco in the galactic open cluster NGC 6231, providing for the first time a full coverage of the orbital period (P = 2.44 days) and a complete analysis of the orbit. This extensive new photometry was analyzed together with multiband spectroscopy and results in an improved ephemeris, photometric elements and absolute parameters of the components. The system is close, but clearly detached. The masses of the components M1 = 16.8 ± 0.5 Mand M2 = 9.4 ± 0.3 Mdo not correspond to the published spectral classification (O9III + B1III). The parameters of the components are consistent with the main-sequence luminosity class. We independently derive a distance modulus V0 − MV = 10.73 ± 0.02.

Mass Segregation in the Globular Cluster Palomar 5 and its Tidal Tails

We present the stellar main-sequence luminosity function (LF) of the disrupted, low-mass, low-concentration globular cluster Palomar 5 and its well-defined tidal tails, which emanate from the cluster as a result of its tidal interaction with the Milky Way. The results of our deep (B ~ 24.5) wide-field photometry unequivocally indicate that preferentially fainter stars were removed from the cluster so that the LF of the cluster's main body exhibits a significant degree of flattening compared with other globular clusters. There is clear evidence of mass segregation, which is reflected in a radial variation of the LFs. The LF of the tidal tails is distinctly enhanced with faint, low-mass stars. Pal 5 exhibits a binary main sequence, and we estimate a photometric binary frequency of roughly 10%. The binaries also show evidence of mass segregation, with more massive binary systems being more strongly concentrated toward the cluster center.

The Lower Main Sequence and Mass Function of the Globular Cluster Messier 4

The deepest optical image ever in a globular star cluster, a Hubble Space Telescope 123 orbit exposure in a single field of Messier 4, was obtained in two filters (F606W, F814W) over a 10 week period in early 2001. A somewhat shallower image obtained in 1995 allowed us to select out cluster and field objects via their proper-motion displacement, resulting in remarkably clean color-magnitude diagrams that reach to V = 30, I = 28. The cluster main-sequence luminosity function contains very few stars fainter than MV = 15.0, MI = 11.8, which, in both filters, is more than 2 mag brighter than our limit. This is about the faintest luminosity seen among field Population II subdwarfs of the same metallicity. However, there remains a sprinkling of potential cluster stars to lower luminosity all the way down to our limiting magnitudes. These latter objects are significantly redder than any known metal-poor field subdwarf. Comparison with the current generation of theoretical stellar models implies that the masses of the lowest luminosity cluster stars observed are near 0.09 M☉. We derive the mass function of the cluster in our field and find that it is very slowly rising toward the lowest masses with no convincing evidence of a turnover even below 0.1 M☉. The formal slope between 0.65 and 0.09 M☉ is α = 0.75 (Salpeter of 2.35) with a 99% confidence interval of 0.55-1.05. A consistency check between these slopes and the number of observed cluster white dwarfs yields a range of possible conclusions, one of which is that we have indeed seen the termination of the white dwarf cooling sequence in M4.

Deep [ITAL]Hubble Space Telescope[/ITAL] WFPC2 Photometry of NGC 288. II. The Main-Sequence Luminosity Function

The main-sequence luminosity function (LF) of the Galactic globular cluster NGC 288 has been obtained using deep Wide Field Planetary Camera 2 photometry. We have employed a new method to correct for completeness and fully account for bin-to-bin migration due to blending and/or observational scatter. The effect of the presence of binary systems in the final LF is quantified and is found to be negligible. There is a strong indication of the mass segregation of unevolved single stars and clear signs of a depletion of low-mass stars in NGC 288 with respect to other clusters. The results are in good agreement with the prediction of theoretical models of the dynamical evolution of NGC 288 that take into account the extreme orbital properties of this cluster.

The Main-Sequence Luminosity Function of Palomar 5 from THE [ITAL]HUBBLE SPACE TELESCOPE[/ITAL

A low mass, large core radius, low central concentration, and strong tidal tails suggest that the globular cluster Palomar 5 has lost a large fraction of its initial mass over time. If the dynamical evolution of Pal 5 has been dominated by the effects of mass loss, then theoretical arguments suggest that the luminosity function should be deficient in low-mass stars. Using deep WFPC2 F555W and F814W photometry, we determine the main-sequence luminosity functions both near the cluster center and in a field near the half-light radius. A comparison of these luminosity functions yields no compelling evidence of mass segregation within the cluster, in accord with expectations for low-concentration clusters. On the other hand, a comparison of the global mass function of Pal 5 with that of ω Cen and M55 indicates an increasing deficiency of stars with progressively lower masses. A fit of the observed luminosity function to theoretical models indicates a mass function for Pal 5 of dN/dm ∝ m-0.5, which is notably more deficient in low-mass stars than other globular clusters that have been studied with the Hubble Space Telescope. The flatness of the mass function is consistent with models of the dynamical evolution of globular clusters that have lost ~90% of their original stellar mass. We suggest that, like NGC 6712, Pal 5 has lost a large percentage of its original stellar content as a result of tidal shocking.

The CFHT Open Star Cluster Survey. III. The White Dwarf Cooling Age of the Rich Open Star Cluster NGC 2099 (M37)

We present deep CCD photometry of the very rich, intermediate-age (similar to the Hyades) open star cluster NGC 2099 (M37). The V, B-V color-magnitude diagram (CMD) for the cluster shows an extremely well-populated and very tightly constrained main sequence extending over 12 mag from the turnoff. Both a well-defined main-sequence turnoff and a red giant population are also clearly evident. The CFH12K photometry for this cluster is faint enough (V ∼ 24.5) to detect the remnants of the most massive progenitor cluster stars under the Type I SNe limit. Therefore, the CMD of the cluster also exhibits a well defined white dwarf "clump" caused by the decreased rate of cooling of these stars as they age, and a subsequent gap with very few objects. By using source classification to eliminate faint blue galaxies and a statistical subtraction technique to eliminate foreground/background objects, we have determined the age of the star cluster from the termination point (MV = 11.95 ± 0.30) in the white dwarf luminosity function. The white dwarf cooling age is found to be 566 ± Myr from comparisons with white dwarf cooling models and is in excellent agreement with the main-sequence turnoff isochrone age (520 Myr). After carefully accounting for the uncertainties in the white dwarf limiting magnitude, we show that the cooling age confirms that models including convective core overshooting are preferred for young–intermediate-aged clusters. This is particularly important in the case of NGC 2099 as the age is similar to that of the Hyades cluster, for which current models have difficulties in reproducing the details of the main-sequence turnoff. We also derive the reddening [E(B-V) = 0.21 ± 0.03] and distance [(m - M)V = 11.55 ± 0.13] to NGC 2099 by matching main-sequence features in the cluster to a new fiducial main sequence for the Hyades, after correcting for small metallicity differences. As a continuing part of the goals of the CFHT Open Star Cluster Survey to better understand dynamical processes of open clusters, we also fit a King model to the cluster density distribution and investigate the cluster main-sequence luminosity and mass functions in increasing concentric annuli. We find some evidence for mass segregation within the boundary of NGC 2099 as expected given the cluster's age relative to the dynamical age. The present global mass function for the cluster is found to be shallower than a Salpeter IMF.

Young Clusters in the Magellanic Clouds. II.

We present the results of a quantitative study of the degree of extension to the boundary of the classical convective core within intermediate mass stars. The basis of our empirical study is the stellar population of four young populous clusters in the Magellanic Clouds which has been detailed in Keller, Bessell & Da Costa (2000). The sample affords a meaningful comparison with theoretical scenarios with varying degrees of convective core overshoot and binary star fraction. Two critical properties of the population, the main-sequence luminosity function and the number of evolved stars, form the basis of our comparison between the observed data set and that simulated from the stellar evolutionary models. On the basis of this comparison we conclude that the case of no convective core overshoot is excluded at a 2 sigma level.

The Main-Sequence Luminosity Function of M13

The color-magnitude diagram and the main-sequence luminosity function of the globular cluster M13 have been investigated. While those clusters observed by the Hubble Space Telescope (HST) show a shallow luminosity function for low-mass stars, M13 has been known to have a very steep gradient toward the faint end. To understand this seemingly unique characteristic of M13, we carried out deep BV CCD observations. The observed field of nearly 56 arcmin2 is located approximately 12' from the cluster center. Our (B-V)-V color-magnitude diagram has the main sequence extended to the detection limit at V ≈ 24.5 mag. It is apparent that there is a significant population of unexpected field stars below V ≈ 22.5, which cannot be accounted for by photometric errors. When these field stars are eliminated, the derived luminosity function of M13 shows a much shallower slope at the faint end, just like other Galactic globular clusters studied by HST observations.