Table of contents

A survey of radio recombination lines in the Galactic plane with longitude −32° < l < +80° and latitude b < ±3° using Ooty Radio Telescope (ORT) at 328 MHz is reported. ORT observations were made using a New Digital Backend (NDB) recently added to the telescope. With the NDB ORT had a beam of 23 × 22 sec(δ) and a passband of ∼1 MHz in the spectral line mode. The above-mentioned Galactic region was divided into ∼2° × 2° patches with the ORT beam pointed to the center. The ORT observations form a study of the distribution of extended low-density warm-ionized medium (ELDWIM) in the inner Galaxy using H271α RLs. By obtaining kinematical distances using V_LSR of the H271α RLs, the distribution of ELDWIM clouds within the inner Galaxy has been deduced for the region given above.

Although the connection of the Chinese "guest" star of 393 AD with the Galactic supernova remnant RX J1713.7-3946 (G347.3-0.5) made by Wang et al. in 1997 is consistent with the remnant's relatively young properties and the guest star's projected position within the "tail" of the constellation Scorpius, there are difficulties with such an association. The brief Chinese texts concerning the 393 AD guest star make no comment about its apparent brightness, stating only that it disappeared after eight months. However, at the remnant's current estimated 1–1.3 kpc distance and A_V ≃ 3, its supernova (SN) should have been a visually bright object at maximum light (−3.5 to −5.0 mag) if M_V = − 17 to −18 and would have remained visible for over a year. The peak brightness ≃0 mag adopted by Wang et al. and others would require the RX J1713.7-3946 supernova to have been a very subluminous event similar to or fainter than SN 2005cs in M51. We also note problems connecting SN 393 with a European record in which the Roman poet Claudian describes a visually brilliant star in the heavens around 393 AD that could be readily seen even in midday. Although several authors have suggested this account may be a reference to the Chinese supernova of 393, Scorpius would not be visible near midday in March when the Chinese first reported the 393 guest star. We review both the Chinese and Roman accounts and calculate probable visual brightnesses for a range of SN subtypes and conclude that neither the Chinese nor the Roman descriptions are easily reconciled with an expected RX J1713.7-3946 supernova brightness and duration.

Main-sequence (MS) and giant late-B and early-A type stars are the best targets for searching for nearby interstellar (IS) Si iv and C iv resonance lines because they are not able to produce them, either in atmospheric layers or in their circumstellar environment, and because many stars of these spectral types are nearby and located in the local interstellar medium (LISM). In addition, the use of certain stars hotter than B6 can lead to misinterpretations (e.g., alpha Arae). This work analyzes the reliable Short-Wavelength Prime high-resolution UV spectra of 558 B6–A9 type stars observed by the International Ultraviolet Explorer at distances lower than 400 pc from the Sun. For the first time, this work utilizes the entire INES database to extract stellar and IS information in a systematic way from homogeneous data. Stars were classified into seven groups: normal (MS and subgiant), giant, peculiar, emission line, Algols, pre-main sequence or Herbig Ae/Be, and shell stars. Only 10 normal stars, located beyond 90 pc, show weak Si iv and C iv absorptions and are clustered around the direction of Sco-Cen, while 85 located closer than 90 pc, as well as another 89 beyond 90 pc, do not show any absorptions at all. We conclude that these highly ionized species originate most probably in the LISM, at 90 pc from the Sun, corresponding to the warm interaction zone (IZ), where the expanding Loop I super-shell and the Local Bubble collide. We base our results on a robust statistical analysis of both spectral types and spatial distributions of the different stellar groups we defined. Our estimated column densities N of both ions are similar to those obtained by other authors for distant stars, suggesting that these absorptions concentrate fundamentally in the IZ. A logarithmic correlation between N and the distance D confirms these results.

B514 is a remote M31 globular cluster (GC) which is located at a projected distance of R_p ≃ 55 kpc. Deep observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate integrated light and star counts of B514. By coupling the analysis of the distribution of the integrated light with star counts, we are able to reliably follow the profile of the cluster out to ∼40''. Based on the combined profile, we study in detail its surface brightness distribution in the F606W and F814W filters and determine its structural parameters by fitting a single-mass isotropic King model. The results showed that the surface brightness distribution departs from the best-fit King model for r > 10''. B514 is quite flat in the inner region and has a larger half-light radius than the majority of normal GCs of the same luminosity. It is interesting that, in the M_V versus log R_h plane, B514 lies nearly on the threshold for ordinary GCs as defined by Mackey & van den Bergh. In addition, B514 was observed as part of the Beijing–Arizona–Taiwan–Connecticut (BATC) Multicolor Sky Survey, using 13 intermediate-band filters covering a wavelength range of 3000–8500 Å. Based on aperture photometry, we obtain its spectral energy distributions (SEDs) as defined by the 13 BATC filters. We determine the cluster's age and mass by comparing its SEDs (from 2267 to 20000 Å, comprised of photometric data from the near-ultraviolet band of the Galaxy Evolution Explorer, 5 Sloan Digital Sky Survey bands, 13 BATC intermediate-band filters, and Two Micron All Sky Survey near-infrared JHK_s filters) with theoretical stellar population synthesis models, resulting in an age of 11.5 ± 3.5 Gyr. This age confirms the previous suggestion that B514 is an old GC in M31. B514 has a mass of 0.96–1.08 × 10⁶ M_☉ and is a medium-mass GC in M31.

We present the first multicolor CCD photometry for the eclipsing binary V380 Cassiopeia (V380 Cas) observed on 34 nights in 2009 and 2010 at the University of Patras Observatory. The PHOEBE program based on the Wilson–Devinney algorithm was used to analyze the first complete BVR_c I_c light curves. It was found that V380 Cas was misclassified and it is a well-detached system consisting of two main-sequence stars. A range of solutions found to give satisfactory fits to the observations is also investigated. The first orbital solution based on the photometric mass ratio q = 1.08 of almost equal temperatures and masses and orbital inclination of i = 8657 was obtained. In addition, based on all available times of light minima, including 12 new ones, a new orbital period of P = 2.714539884 days is given.

We present a catalog of 80 very wide fragile binary candidates (projected separations >10,000 AU) from the Sloan Digital Sky Survey Data Release Eight spectral archive. The pairs were selected based on proper motion, radial velocity, metallicity, and photometric parallax criteria. The angular separations of these pairs range from 3'' to 250''. The peak in the metallicity distribution of these pairs is about −0.5 dex of solar metallicity. Space motions and reduced proper motion diagrams indicate that all these pairs are members of the disk. The chromospheric activity index S_HK of each component in 38 binary candidates having spectra of high signal-to-noise ratio and member stars of three open clusters (NGC 2420, M67, and NGC 6791) were measured. The S_HK versus color relation for these binary candidates is consistent with the trend seen in these open clusters. The ages implied by this relation suggest that fragile wide pairs can survive longer than 8 Gyr.

We have used the Very Large Array to study the Zeeman effect in 21 cm H i absorption lines from two star-forming regions in the Cygnus X complex, DR 22 and ON 2. We measure the line-of-sight magnetic field toward these regions, finding B_los = −84 ± 11 μG toward the DR 22 H ii region and B_los < 50 μG toward each of the two H ii regions in ON 2. We interpret these results in terms of two different models. In one model, we assume that the H i Zeeman effect is a measure of magnetic fields in the associated molecular clouds. If so, then the DR 22 molecular cloud is magnetically subcritical, that is, magnetically dominated. The ON 2 molecular clouds are magnetically supercritical. In a second model, we assume that the H i Zeeman effect is a measure of magnetic fields in photon-dominated regions where the gas has been compressed (and the field amplified) by absorption of stellar radiation. We find that this second model, where the measured field strength has been affected by star formation, accounts well for the DR 22 H i Zeeman effect. This same model, however, overpredicts the magnetic field in ON 2. ON 2 may be a region where the magnetic field is energetically insignificant or where the field happens to lie nearly in the plane of the sky.

Faraday rotation measure synthesis is a method for analyzing multichannel polarized radio emissions, and it has emerged as an important tool in the study of Galactic and extragalactic magnetic fields. The method requires the recovery of the Faraday dispersion function from measurements restricted to limited wavelength ranges, which is an ill-conditioned deconvolution problem. Here, we discuss a recovery method that assumes a sparse approximation of the Faraday dispersion function in an overcomplete dictionary of functions. We discuss the general case when both thin and thick components are included in the model, and we present the implementation of a greedy deconvolution algorithm. We illustrate the method with several numerical simulations that emphasize the effect of the covered range and sampling resolution in the Faraday depth space, and the effect of noise on the observed data.

Multiband CCD photometric observations of SZ Her were obtained between 2008 February and May. The light curve was completely covered and indicated a significant temperature difference between both components. The light-curve synthesis presented in this paper indicates that the eclipsing binary is a classical Algol-type system with parameters of q = 0.472, i = 8757, and Δ(T₁ – T₂) = 2381 K; the primary component fills approximately 77% of its limiting lobe and is slightly larger than the lobe-filling secondary component. More than 1100 times of minimum light spanning more than a century were used to study an orbital behavior of the binary system. It was found that the orbital period of SZ Her varied due to a combination of two periodic variations with cycle lengths of P₃ = 85.8 yr and P₄ = 42.5 yr and semi-amplitudes of K₃ = 0.013 days and K₄ = 0.007 days, respectively. The most reasonable explanation for these variations is a pair of light-time effects driven by the possible existence of two M-type companions with minimum masses of M₃ = 0.22 M_☉ and M₄ = 0.19 M_☉ that are located close to the 2:1 mean motion resonance. If two additional bodies exist, then the overall dynamics of the multiple system may provide a significant clue to the formation and evolution of the eclipsing pair.

We observed a sample of 1536 sources with correlated flux densities brighter than 200 mJy at 8 GHz with the very long baseline interferometry (VLBI) array VLBI Exploration of Radio Astrometry at 22 GHz. One half of the target sources has been detected. The detection limit was around 200 mJy. We derived the correlated flux densities of 877 detected sources in three ranges of projected baseline lengths. The objective of these observations was to determine the suitability of given sources as phase calibrators for dual-beam and phase-referencing observations at high frequencies. Preliminary results indicate that the number of compact extragalactic sources at 22 GHz brighter than a given correlated flux density level is two times less than that at 8 GHz.

We collected almost all of the Galactic infrared carbon stars (IRCSs) from literature published up to the present to organize a catalog of 974 Galactic IRCSs in this paper. Some of their photometric properties in the near-, mid-, and far-infrared are discussed.

Archival spectra from the Sloan Digital Sky Survey of two optically faint flat-spectrum protostars, IRAS 04369+2539 and IRAS 05451+0037, show strong emission-line features including—notably—clear and broad emission across several molecular bands of TiO and VO. The molecular emission is indicative of dense, warm circumstellar gas and has been seen previously in only one object: the flat-spectrum protostar IRAS 20496+4354 during a strong optical outburst (PTF 10nvg). The presence of broad molecular emission features in two additional objects having similar mid-infrared properties (but not known to be undergoing outbursts) could provide new insight into phases of rapid accretion/outflow at early stages of the protoplanetary disk. At present, the relevant geometry and the formation or heating mechanisms responsible for the observed TiO/VO cooling emission remain unexplained.

This paper describes the image stacks and catalogs of the Canada–France–Hawaii Telescope Legacy Survey produced using the MegaPipe data pipeline at the Canadian Astronomy Data Centre. The Legacy Survey is divided into two parts. The Deep Survey consists of four fields each of 1 deg², with magnitude limits (50% completeness for point sources) of u = 27.5, g = 27.9, r = 27.7, i = 27.4, and z = 26.2. It contains 1.6 × 10⁶ sources. The Wide Survey consists of 150 deg² split over four fields, with magnitude limits of u = 26.0, g = 26.5, r = 25.9, i = 25.7, and z = 24.6. It contains 3 × 10⁷ sources. This paper describes the calibration, image stacking, and catalog generation process. The images and catalogs are available on the web through several interfaces: normal image and text file catalog downloads, a "Google Sky" interface, an image cutout service, and a catalog database query service.

In this paper, we present the results of searching the Kepler Q2 public data set for the secondary eclipses of 76 hot Jupiter planet candidates from the list of 1235 candidates published by Borucki et al. This search has been performed by modeling both the Kepler pre-search data conditioned light curves and new light curves produced via our own photometric pipeline. We derive new stellar and planetary parameters for each system, while calculating robust errors for both. We find 16 systems with 1σ–2σ, 14 systems with 2σ–3σ, and 6 systems with >3σ confidence level secondary eclipse detections in at least one light curve produced via the Kepler pre-search data conditioned light curve or our own pipeline; however, results can vary depending on the light curve modeled and whether eccentricity is allowed to vary or not. We estimate false alarm probabilities of 31%, 10%, and 6% for the 1σ–2σ, 2σ–3σ, and >3σ confidence intervals, respectively. Comparing each secondary eclipse result to theoretical expectations, we find that the majority of detected planet candidates emit more light than expected owing to thermal blackbody emission in the optical Kepler bandpass, and present a trend of increasing excess emission with decreasing maximum effective planetary temperature. These results agree with previously published optical secondary eclipse data for other hot Jupiters. We explore modeling biases, significant planetary albedos, non-local thermodynamic equilibrium or other thermal emission, significant internal energy generation, and misidentification of brown dwarfs, low-mass stars, or stellar blends as possible causes of both the excess emission and its correlation with expected planetary temperature. Although we find that no single cause is able to explain all of the planet candidates, significant planetary albedos, with a general trend of increasing planetary albedos with decreasing atmospheric temperatures, are able to explain most of the systems. Identifying systems that we deem likely to be low-mass stars or stellar blends, we estimate an 11% false-positive rate in the current Kepler planet candidate sample of hot Jupiters. We also establish robust upper limits on the eclipse depth for the remaining systems and find that the emission of a significant fraction of these systems is consistent with the planets having very low albedos, i.e., at least 30% of all systems have A_g < 0.3 at 1σ confidence levels. This result augments the current number of constrained exoplanetary albedos and extends the sample of low albedo determinations to planets with temperatures as low as 1200 K. Finally, we note that continued observations with the Kepler spacecraft and improved techniques for the removal of systematic noise in the Kepler data are needed to better characterize these systems.

The baryonic Tully–Fisher relation (BTFR) is an empirical relation between baryonic mass and rotation velocity in disk galaxies. It provides tests of galaxy formation models in ΛCDM and of alternative theories like modified Newtonian dynamics (MOND). Observations of gas-rich galaxies provide a measure of the slope and normalization of the BTFR that is more accurate (if less precise) than that provided by star-dominated spirals, as their masses are insensitive to the details of stellar population modeling. Recent independent data for such galaxies are consistent with M_b = AV⁴_f with A = 47 ± 6 M_☉ km⁻⁴ s⁴. This is equivalent to MOND with a₀ = 1.3 ± 0.3 Å s⁻². The scatter in the data is consistent with being due entirely to observational uncertainties. It is unclear why the physics of galaxy formation in ΛCDM happens to pick out the relation predicted by MOND. We introduce a feedback efficacy parameter $\mathcal {E}$ to relate halo properties to those of the galaxies they host. $\mathcal {E}$ correlates with star formation rate and gas fraction in the sense that galaxies that have experienced the least star formation have been most impacted by feedback.

We present new UBVI_c CCD photometry of the young open clusters Trumpler 14 (Tr 14) and Trumpler 16 (Tr 16) in the η Carina Nebula. We also identify the optical counterpart of Chandra X-ray sources and Two Micron All Sky Survey point sources. The members of the clusters were selected from the proper-motion study, spectral types, reddening characteristics, and X-ray or near-IR excess emission. An abnormal reddening law R_{V, cl} = 4.4  ±  0.2 was obtained for the stars in the η Carina Nebula using the 141 early-type stars with high proper-motion membership probability (P_μ ≧ 70%). We determined the distance to each cluster and conclude that Tr 14 and Tr 16 have practically the same distance modulus of V₀ − M_V = 12.3 ± 0.2 mag (d = 2.9 ± 0.3 kpc). The slope of the initial mass function was determined to be Γ = −1.3 ± 0.1 for Tr 14, Γ = −1.3 ± 0.1 for Tr 16, and Γ = −1.4 ± 0.1 for all members in the observed region for the stars with log m≧0.2. We also estimated the age of the clusters to be about 1–3 Myr from the evolutionary stage of evolved stars and low-mass pre-main-sequence stars.

We report on the results of speckle observations at the 4.1 m SOAR telescope in 2010 and 2011. A total of 639 objects were observed. We give 562 measurements of 418 resolved binaries, including 21 pairs resolved for the first time, and upper detection limits for 221 unresolved stars. New orbital elements have been determined for 42 physical pairs, of which 22 are first-time calculations; the rest are corrections, sometimes substantial. Linear elements are calculated for nine apparently optical doubles. We comment on new pairs, new orbital solutions, and other remarkable objects.

We present a near-infrared study focused on the detection and characterization of the youngest stellar component of the NGC 604 giant star-forming region in the Triangulum galaxy (M 33). By means of color–color diagrams derived from the photometry of JHK_s images taken with the Gemini Near Infrared Imaging and Spectrometer (NIRI), we have found 68 candidate massive young stellar objects. The spatial distribution of these sources matches the areas where previous studies suggested that star formation might be taking place, and the high spatial resolution of our deep NIRI imaging allows us to pinpoint the star-forming knots. An analysis of the fraction of objects that show infrared excess suggests that the star formation is still active, supporting the presence of a second generation of stars being born, although the evidence for or against sequential star formation does not seem to be conclusive.

Adopting the SPECTRUM package, which is a stellar spectral synthesis program, we have synthesized a comprehensive set of 2890 near-infrared (NIR) synthetic spectra with a resolution and wavelength sampling similar to the Sloan Digital Sky Survey (SDSS) and the forthcoming Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra. During the synthesis, we applied the "New grids of ATLAS9 Model Atmosphere" to develop a grid of local thermodynamic equilibrium model atmospheres for effective temperatures (T_eff) ranging from 3500 to 7500 K, for surface gravities (log g) from 0.5 to 5.0 dex, for metallicities ([Fe/H]) from −4.0 to 0.5 dex, and for solar ([α/Fe] = 0.0 dex) and non-solar ([α/Fe] = +0.4 dex) abundances. This synthetic stellar library is composed of 1350 solar scaled abundance (SSA) and 1530 non-solar scaled abundance (NSSA) spectra, grounding on which we have defined a new set of NIR Ca ii triplet indices and an index CaT as the sum of the three. These defined indices were automatically measured on every spectrum of the synthetic stellar library and calibrated with the indices computed on the observational spectra from the INDO-U.S. stellar library. In order to check the effect of α-element enhancement on the so-defined Ca ii indices, we compared indices measured on the SSA spectra with those on the NSSA ones at the same trine of stellar parameters (T_eff, log g, [Fe/H]); luckily, little influences of α-element enhancement were found. Furthermore, comparisons of our synthetic indices with the observational ones from measurements on the INDO-U.S. stellar library, the SDSS-DR7 and SDSS-DR8 spectroscopic survey are presented, respectively, for dwarfs and giants in specific. For dwarfs, our synthetic indices could well reproduce the behaviors of the observational indices versus stellar parameters, which verifies the validity of our index definitions for dwarfs. For giants, the consistency between our synthetic indices and the observational ones does not appear to be as good. However, a new synthetic library of NIR Ca ii indices has been founded for deeper studies on the NIR wave band of stellar spectra, and this library is particularly appropriate for the SDSS and the forthcoming LAMOST stellar spectra. We have regressed the strength of the CaT index as a function of stellar parameters for both dwarfs and giants after a series of experimental investigations into relations of the indices with stellar parameters. For dwarfs, log g has little effect on the indices, while [Fe/H] and T_eff play a role together. The leading factor is probably [Fe/H], which changes the strength of the indices by a positive trend. For giants, log g starts to influence the strength of the indices by a negative trend for the metal-poor, and even impact deeply for the metal-rich; besides, [Fe/H] and T_eff still matter. In addition, we briefly discussed the major differences between our Ca ii triplet indices and the CaHK doublet indices. Ultimately, a supplemental experiment was carried out to show that spectral noises do have effects on our set of NIR Ca ii indices. However, the influence is not weak enough to be ignored if the signal-to-noise ratio falls below 20.

Radio recombination line (RRL or RL for short) observations from 10 Galactic positions using the Ooty Radio Telescope (ORT) at 328 MHz and the Westerbork Synthesis Radio Telescope (WSRT) at 1.4 GHz have been presented. ORT observations were made using a recently augmented New Digital Backend (NDB). NDB offered a bandwidth of 1 MHz that was used to observe H271α RL. The eight intermediate-frequency bands offered by WSRT in the incoherent addition mode were used to detect the seven H/Henα RLs with n = 165–171 and the H208β RL. RL observations common to WSRT and ORT have been put together to model the diffuse low-density ionized gas (extended low density warm ionized medium, ELDWIM). This modeling constrains the electron number density in ELDWIM to 1.0 cm⁻³ < n_e < 10.0 cm⁻³ for a temperature range of 10³–10⁴ K for these 10 positions. An effective stellar temperature of the H ii region picture for three positions showing He line detection has been presented using spherical cloud modeling. The lower limits on the stellar temperatures are >33,000 K for the obtained ratios of N_{He +}/N_{H +} toward these directions.

We present UBV photometry of the highly reddened and poorly studied open cluster Berkeley 55, revealing an important population of B-type stars and several evolved stars of high luminosity. Intermediate-resolution far-red spectra of several candidate members confirm the presence of one F-type supergiant and six late supergiants or bright giants. The brightest blue stars are mid-B giants. Spectroscopic and photometric analyses indicate an age 50 ± 10 Myr. The cluster is located at a distance d ≈ 4 kpc, consistent with other tracers of the Perseus Arm in this direction. Berkeley 55 is thus a moderately young open cluster with a sizable population of candidate red (super)giant members, which can provide valuable information about the evolution of intermediate-mass stars.

We have studied multi-band surface brightness profiles of a representative sample of 34 nearby dwarf irregular galaxies. Our data include Galaxy Evolution Explorer (GALEX) FUV/NUV, UBV, and Hα and Spitzer 3.6 μm images. These galaxies constitute the majority of the LITTLE THINGS survey (Local Irregulars That Trace Luminosity Extremes—The H i Nearby Galaxy Survey). By modeling the azimuthal averages of the spectral energy distributions with a complete library of star formation histories, we derived the stellar mass surface density distributions and the star formation rate averaged over three different timescales: the recent 0.1 Gyr, 1 Gyr, and a Hubble time. We find that, for ∼80% (27 galaxies) of our sample galaxies, radial profiles (at least in the outer part) at shorter wavelengths, corresponding to younger stellar populations, have shorter disk scale lengths than those at longer wavelengths, corresponding to older stellar populations. This indicates that the star-forming disk has been shrinking. In addition, the radial distributions of the stellar mass surface density are well described as piece-wise exponential profiles, and ∼80% of the galaxies have steeper mass profiles in the outer disk than in the inner region. The steep radial decline of the star formation rate in the outer parts compared to that in the inner disks gives a natural explanation for the down-bending stellar mass surface density profiles. Within the inner disks, our sample galaxies on average have constant ratios of recent star formation rate to stellar mass with radius. Nevertheless, ∼35% (12 galaxies, among which 7 have baryonic mass ≲10⁸ M_☉) of the sample exhibit negative slopes across the observed disk, which is in contrast with the so-called inside–out disk growth scenario suggested for luminous spiral galaxies. The tendency of star formation to become concentrated toward the inner disks in low-mass dwarf irregular galaxies is interpreted as a result of their susceptibility to environmental effects and regulation through stellar feedback.

We present the first metallicity distribution functions of the old field populations in the Magellanic Clouds (MCs). Our metallicities are based on the Fourier decomposition of Type ab RR Lyrae light curves from the Optical Gravitational Lensing Experiment. On the metallicity scale of Zinn & West, we find a mean metallicity of [Fe/H] = −1.50 ± 0.24 dex based on 16,776 RR Lyrae stars in the Large Magellanic Cloud (LMC). For the Small Magellanic Cloud (SMC) we obtain −1.70 ± 0.27 dex based on 1831 RR Lyrae stars. These uncertainties represent the intrinsic spread in the population rather than the standard deviation of the mean. Our results are in good agreement with the few existing spectroscopic metallicity determinations for LMC RR Lyrae stars from the literature. For both the LMC and the SMC the metallicity spread exceeds 1 dex in [Fe/H]. The distribution of metallicities in both Clouds is very uniform, and no significant metallicity gradient is detectable. We also do not find any pronounced populations of extremely metal-poor RR Lyrae candidates with metallicities well below −2 dex, although we need to caution that the photometric method used may overestimate the metallicities of metal-deficient stars. Moreover, because of stellar evolutionary effects one does not expect to observe many RR Lyrae stars among very metal-poor horizontal branch stars. We suggest that the MCs experienced fairly rapid and efficient early enrichment involving pre-enriched gas as well as possibly gas infall, while metal loss through outflows does not seem to have played a significant role. Moreover, we suggest that the differences in the metallicities of the old population of LMC and SMC make an origin from a single, common progenitor unlikely, unless the separation happened very early on.

We investigate the connection between starburst and active galactic nucleus (AGN) activity by comparing 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission with AGN properties. Utilizing the slitless spectroscopic capability of the AKARI space telescope, we observe a moderate-luminosity Type I AGN at z ∼ 0.4 to measure global starburst activity. The 3.3 μm PAH emissions are detected for 7 out of 26 target galaxies. We find no strong correlation between the 3.3 μm PAH emission and AGN luminosity in the limited range of the observed AGN luminosity, suggesting that global star formation may not be closely related to AGN activity. Combining our measurements with previous 3.3 μm measurements of low-redshift Type I AGNs in the literature, we investigate the connection between nuclear starburst and AGN activity. In contrast to global star formation, the 3.3 μm PAH luminosity measured from the central part of galaxies correlates with AGN luminosity, implying that starburst activity and AGN activity are directly connected in the nuclear region.

We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs (WDs) to pure hydrogen atmosphere WD models. Our photometric data set is obtained from a 121-orbit Hubble Space Telescope program using the Wide Field Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images. These images cover more than 60 arcmin² and extend over a radial range of 5–13.7 arcmin (6.5–17.9 pc) within the globular cluster. Using a likelihood analysis, we obtain a best-fitting unreddened distance modulus of (m − M)_o = 13.36 ± 0.02 ± 0.06 corresponding to a distance of 4.69 ± 0.04 ± 0.13 kpc, where the first error is random and the second is systematic. We also search the WD photometry for infrared excess in the F160W filter, indicative of low-mass companions, and find no convincing cases within our sample.

Continuum fitting is an important aspect of Lyα forest science, since errors in the derived optical depths scale with the fractional continuum error. However, traditional methods of estimating continua in noisy and moderate-resolution spectra (e.g., Sloan Digital Sky Survey, SDSS; S/N ≲ 10 pixel⁻¹ and R ∼ 2000), such as power-law extrapolation or dividing by the mean spectrum, achieve no better than ∼15% rms accuracy. To improve on this, we introduce mean-flux-regulated principal component analysis (MF-PCA) continuum fitting. In this technique, PCA fitting is carried out redward of the quasar Lyα line in order to provide a prediction for the shape of the Lyα forest continuum. The slope and amplitude of this continuum prediction is then corrected using external constraints for the Lyα forest mean flux. This requires prior knowledge of the mean flux, 〈F〉, but significantly improves the accuracy of the flux transmission, F ≡ exp (− τ), estimated from each pixel. From tests on mock spectra, we find that MF-PCA reduces the errors to 8% rms in S/N ∼ 2 spectra, and <5% rms in spectra with S/N ≳ 5. The residual Fourier power in the continuum is decreased by a factor of a few in comparison with dividing by the mean continuum, enabling Lyα flux power spectrum measurements to be extended to ∼2 × larger scales. Using this new technique, we make available continuum fits for 12,069 z > 2.3 Lyα forest spectra from SDSS Data Release 7 for use by the community. This technique is also applicable to future releases of the ongoing Baryon Oscillations Spectroscopic Survey, which obtains spectra for ∼150, 000 Lyα forest spectra at low signal-to-noise (S/N ∼ 2).

We use Hubble Space Telescope imaging to show that the nearby dwarf starburst galaxy NGC 4449 has an unusual abundance of luminous red star clusters. Joint constraints from integrated photometry, low-resolution spectroscopy, dynamical mass-to-light ratios, and resolved color–magnitude diagrams provide evidence that some of these clusters are old globular clusters (GCs). Spectroscopic data for two massive clusters suggest intermediate metallicities ([Fe/H] ∼−1) and subsolar Mg enhancement ([Mg/Fe] ∼−0.1 to −0.2). One of these clusters may be the nucleus of a tidally disrupting dwarf galaxy; the other is very massive (∼3 × 10⁶ M_☉). We have also identified a population of remote halo GCs. NGC 4449 is consistent with an emerging picture of the ubiquity of stellar halos among dwarf galaxies, and study of its GCs may help distinguish between accretion and in situ scenarios for such halos.

We present a new technique for calibrating the primary beam of a wide-field, drift-scanning antenna element. Drift-scan observing is not compatible with standard beam calibration routines, and the situation is further complicated by difficult-to-parameterize beam shapes and, at low frequencies, the sparsity of accurate source spectra to use as calibrators. We overcome these challenges by building up an interrelated network of source "crossing points"—locations where the primary beam is sampled by multiple sources. Using the single assumption that a beam has 180° rotational symmetry, we can achieve significant beam coverage with only a few tens of sources. The resulting network of crossing points allows us to solve for both a beam model and source flux densities referenced to a single calibrator source, circumventing the need for a large sample of well-characterized calibrators. We illustrate the method with actual and simulated observations from the Precision Array for Probing the Epoch of Reionization.