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We measure the color and stellar mass dependence of clustering in spectroscopic galaxies at 0.6 < z < 0.65 using data from the Baryon Oscillation Spectroscopic Survey component of the Sloan Digital Sky Survey. We greatly increase the statistical precision of our clustering measurements by using the cross-correlation of 66,657 spectroscopic galaxies to a sample of 6.6 million fainter photometric galaxies. The clustering amplitude w(R) is measured as the ratio of the mean excess number of photometric galaxies found within a specified radius annulus around a spectroscopic galaxy to that from a random photometric galaxy distribution. We recover many of the familiar trends at high signal-to-noise ratio. We find the ratio of the clustering amplitudes of red and blue massive galaxies to be in our smallest annulus of 75–125 kpc. At our largest radii (2–4 Mpc), we find . Red galaxies therefore have denser environments than their blue counterparts at z ∼ 0.625, and this effect increases with decreasing radius. Irrespective of color, we find that w(R) does not obey a simple power-law relation with radius, showing a dip around 1 Mpc. Holding stellar mass fixed, we find a clear differentiation between clustering in red and blue galaxies, showing that clustering is not solely determined by stellar mass. Holding color fixed, we find that clustering increases with stellar mass, especially for red galaxies at small scales (more than a factor of 2 effect over 0.75 dex in stellar mass). [ABSTRACT FROM AUTHOR]

We present 29 likely members of the young ρ Oph or Upper Sco regions of recent star formation that exhibit “accretion burst” type light curves in K2 time series photometry. The bursters were identified by visual examination of their ∼80-day light curves, though all satisfy the flux asymmetry criterion for burst behavior defined by Cody et al. The burst sources represent ≈9% of cluster members with strong infrared excess indicative of circumstellar material. Higher amplitude burster behavior is correlated with larger inner disk infrared excesses, as inferred from WISE color. The burst sources are also outliers in their large Hα emission equivalent widths. No distinction between bursters and non-bursters is seen in stellar properties such as multiplicity or spectral type. The frequency of bursters is similar between the younger, more compact ρ Oph region, and the older, more dispersed Upper Sco region. The bursts exhibit a range of shapes, amplitudes (∼10%–700%), durations (∼1–10 days), repeat timescales (∼3–80 days), and duty cycles (∼10%–100%). Our results provide important input to models of magnetospheric accretion, in particular, by elucidating the properties of accretion-related variability in the low state between major longer duration events such as EX Lup and FU Ori type accretion outbursts. We demonstrate the broad continuum of accretion burst behavior in young stars—extending the phenomenon to lower amplitudes and shorter timescales than traditionally considered in the theory of pre-main sequence accretion history. [ABSTRACT FROM AUTHOR]

N103B is a Type Ia supernova remnant (SNR) projected in the outskirts of the superbubble around the rich cluster NGC 1850 in the Large Magellanic Cloud (LMC). We have obtained Hα and continuum images of N103B with the Hubble Space Telescope (HST) and high-dispersion spectra with the 4 m and 1.5 m telescopes at Cerro Tololo Inter-American Observatory. The HST Hα image exhibits a complex system of nebular knots inside an incomplete filamentary elliptical shell that opens to the east, where X-ray and radio emission extends farther out. Electron densities of the nebular knots, determined from the [S ii] doublet, reach 5300 cm−3, indicating an origin of circumstellar medium, rather than interstellar medium. The high-dispersion spectra reveal three kinematic components in N103B: (1) a narrow component with [N ii] λ6583/Hα ∼ 0.14 from the ionized interstellar gas associated with the superbubble of NGC 1850 in the background, (2) a broader Hα component with no [N ii] counterpart from the SNR’s collisionless shocks into a mostly neutral ambient medium, and (3) a broad component, ∼ 500 km s−1, in both Hα and [N ii] lines from shocked material in the nebular knots. The Balmer-dominated filaments can be fitted by an ellipse, and we adopt its center as the site of SN explosion. We find that the star closest to this explosion center has colors and luminosity consistent with a 1 surviving subgiant companion as modeled by Podsiadlowski. Follow-up spectroscopic observations are needed to confirm this star as the SN’s surviving companion. [ABSTRACT FROM AUTHOR]

We use deep optical photometry from the Next Generation Virgo Cluster Survey (NGVS) to investigate the color–magnitude diagram for the galaxies inhabiting the core of this cluster. The sensitivity of the NGVS imaging allows us to continuously probe galaxy colors over a factor of ∼2 × 105 in luminosity, from brightest cluster galaxies to scales overlapping classical satellites of the Milky Way ( ∼ −9; M* ∼ 106M⊙), within a single environment. Remarkably, we find the first evidence that the red sequence (RS) flattens in all colors at the faint-magnitude end (starting between −14 ≤ ≤ −13, around M* ∼ 4 × 107M⊙), with the slope decreasing to ∼60% or less of its value at brighter magnitudes. This could indicate that the stellar populations of faint dwarfs in Virgo’s core share similar characteristics (e.g., constant mean age) over ∼3 mag in luminosity, suggesting that these galaxies were quenched coevally, likely via pre-processing in smaller hosts. We also compare our results to galaxy formation models, finding that the RS in model clusters have slopes at intermediate magnitudes that are too shallow, and in the case of semianalytic models, do not reproduce the flattening seen at both extremes (bright/faint) of the Virgo RS. Deficiencies in the chemical evolution of model galaxies likely contribute to the model-data discrepancies at all masses, while overly efficient quenching may also be a factor at dwarf scales. Deep UV and near-IR photometry are required to unambiguously diagnose the cause of the faint-end flattening. [ABSTRACT FROM AUTHOR]

We present a study of the continuum polarization over the 400–600 nm range of 19 SNe Ia obtained with FORS at the VLT. We separate them into those that show Na i D lines at the velocity of their hosts and those that do not. Continuum polarization of the sodium sample near maximum light displays a broad range of values, from extremely polarized cases like SN 2006X to almost unpolarized ones like SN 2011ae. The non-sodium sample shows, typically, smaller polarization values. The continuum polarization of the sodium sample in the 400–600 nm range is linear with wavelength and can be characterized by the mean polarization (). Its values span a wide range and show a linear correlation with color, color excess, and extinction in the visual band. Larger dispersion correlations were found with the equivalent width of the Na i D and Ca ii H and K lines, and also a noisy relation between and RV, the ratio of total to selective extinction. Redder SNe show stronger continuum polarization, with larger color excesses and extinctions. We also confirm that high continuum polarization is associated with small values of RV. The correlation between extinction and polarization—and polarization angles—suggest that the dominant fraction of dust polarization is imprinted in interstellar regions of the host galaxies. We show that Na i D lines from foreground matter in the SN host are usually associated with non-galactic ISM, challenging the typical assumptions in foreground interstellar polarization models. [ABSTRACT FROM AUTHOR]

We present a revised Tip of the Red Giant Branch (TRGB) calibration, accurate to 2.7% of distance. A modified TRGB magnitude corrected for its color dependence, the QT magnitude, is introduced for better measurement of the TRGB. We determine the color–magnitude relation of the TRGB from photometry of deep images of HST/ACS fields around eight nearby galaxies. The zero-point of the TRGB at the fiducial metallicity ([Fe/H] = −1.6 ()) is obtained from photometry of two distance anchors, NGC 4258 (M106) and the Large Magellanic Cloud (LMC), to which precise geometric distances are known: MQT,TRGB = −4.023 ± 0.073 mag from NGC 4258 and MQT,TRGB = −4.004 ± 0.096 mag from the LMC. A weighted mean of the two zero-points is MQT,TRGB = −4.016 ± 0.058 mag. Quoted uncertainty is ∼2× smaller than those of previous calibrations. We compare the empirical TRGB calibration derived in this study with theoretical stellar models, finding that there are significant discrepancies, especially for red color (). We provide the revised TRGB calibration in several magnitude systems for future studies. [ABSTRACT FROM AUTHOR]

Up-to-date isochrones, zero-age horizontal-branch (ZAHB) loci, and evolutionary tracks for core He-burning stars are applied to the color–magnitude diagrams of M3, M15, and M92, focusing in particular on their RR Lyrae populations. Periods for the ab- and c-type variables are calculated using the latest theoretical calibrations of and as a function of luminosity, mass, effective temperature (), and metallicity. Our models are generally able to reproduce the measured periods to well within the uncertainties implied by the stellar properties on which pulsation periods depend, as well as the mean periods and cluster-to-cluster differences in and , on the assumption of well-supported values of , , and [Fe/H]. While many of RR Lyrae in M3 lie close to the same ZAHB that fits the faintest horizontal-branch (HB) stars at bluer or redder colors, the M92 variables are all significantly evolved stars from ZAHB locations on the blue side of the instability strip. M15 appears to contain a similar population of HB stars as M92, along with additional helium-enhanced populations not present in the latter which comprise most of its RR Lyrae stars. The large number of variables in M15 and the similarity of the observed values of and in M15 and M92 can be explained by HB models that allow for variations in Y. Similar ages (∼12.5 Gyr) are found for all three clusters, making them significantly younger than the field halo subgiant HD 140283. Our analysis suggests a preference for stellar models that take diffusive processes into account. [ABSTRACT FROM AUTHOR]

The combination of spectroscopic stellar metallicities and resolved star color–magnitude diagrams (CMDs) has the potential to constrain the entire star formation history (SFH) of a galaxy better than fitting CMDs alone (as is most common in SFH studies using resolved stellar populations). In this paper, two approaches to incorporating external metallicity information into CMD-fitting techniques are presented. Overall, the joint fitting of metallicity and CMD information can increase the precision of measured age–metallicity relationships (AMRs) and star formation rates by 10% over CMD fitting alone. However, systematics in stellar isochrones and mismatches between spectroscopic and photometric determinations of metallicity can reduce the accuracy of the recovered SFHs. I present a simple mitigation of these systematics that can reduce their amplitude to the level obtained from CMD fitting alone, while ensuring that the AMR is consistent with spectroscopic metallicities. As is the case in CMD-fitting analysis, improved stellar models and calibrations between spectroscopic and photometric metallicities are currently the primary impediment to gains in SFH precision from jointly fitting stellar metallicities and CMDs. [ABSTRACT FROM AUTHOR]

The article presents information on the colors of the stars in globular clusters. Elliptical galaxies are believed to form from the mergers of a few smaller galaxies. Most ellipticals are surrounded by a cloud of very old globular star clusters. Over the last decade, the color distribution of the clusters in most ellipticals was indeed found to be bimodal. This bimodal color distribution was an exciting confirmation of the current ideas about galaxy formation, but this confirmation is now less secure. From the time of its discovery, the bimodal color distribution of the clusters in elliptical galaxies was interpreted as a bimodal metallicity distribution. The interpretation of the bimodal colors depends on the true shape of the color-metallicity relation. Researchers have made new theoretical stellar population synthesis models for clusters, and have also collated observations from the literature. Their theoretical color-metallicity relations agree very well with the observations. The fraction of clusters in each color mode, and the mean colors of the modes, are observed to vary with the brightness of the host galaxy.

We use the Zurich Environmental Study database to investigate the environmental dependence of the merger fraction Γ and merging galaxy properties in a sample of ∼1300 group galaxies with M > 109.2M☼ and 0.05 < z < 0.0585. In all galaxy mass bins investigated in our study, we find that Γ decreases by a factor of ∼2-3 in groups with halo masses MHALO > 1013.5M☼ relative to less massive systems, indicating a suppression of merger activity in large potential wells. In the fiducial case of relaxed groups only, we measure a variation of ΔΓ/Δlog (MHALO) ∼ –0.07 dex–1, which is almost independent of galaxy mass and merger stage. At galaxy masses >1010.2M☼, most mergers are dry accretions of quenched satellites onto quenched centrals, leading to a strong increase of Γ with decreasing group-centric distance at these mass scales. Both satellite and central galaxies in these high-mass mergers do not differ in color and structural properties from a control sample of nonmerging galaxies of equal mass and rank. At galaxy masses of <1010.2M☼ where we mostly probe satellite-satellite pairs and mergers between star-forming systems close pairs (projected distance <10-20 kpc) show instead ∼2 × enhanced (specific) star formation rates and ∼1.5 × larger sizes than similar mass, nonmerging satellites. The increase in both size and star formation rate leads to similar surface star formation densities in the merging and control-sample satellite populations. [ABSTRACT FROM AUTHOR]

We investigate the statistical dependence of the peak intrinsic colors of Type Ia supernovae (SNe Ia) on their expansion velocities at maximum light, measured from the Si II λ6355 spectral feature. We construct a new hierarchical Bayesian regression model, accounting for the random effects of intrinsic scatter, measurement error, and reddening by host galaxy dust, and implement a Gibbs sampler and deviance information criteria to estimate the correlation. The method is applied to the apparent colors from BVRI light curves and Si II velocity data for 79 nearby SNe Ia. The apparent color distributions of high-velocity (HV) and normal velocity (NV) supernovae exhibit significant discrepancies for B – V and B – R, but not other colors. Hence, they are likely due to intrinsic color differences originating in the B band, rather than dust reddening. The mean intrinsic B – V and B – R color differences between HV and NV groups are 0.06 ± 0.02 and 0.09 ± 0.02 mag, respectively. A linear model finds significant slopes of –0.021 ± 0.006 and –0.030 ± 0.009 mag (103 km s–1)–1 for intrinsic B – V and B – R colors versus velocity, respectively. Because the ejecta velocity distribution is skewed toward high velocities, these effects imply non-Gaussian intrinsic color distributions with skewness up to +0.3. Accounting for the intrinsic-color-velocity correlation results in corrections to AV extinction estimates as large as –0.12 mag for HV SNe Ia and +0.06 mag for NV events. Velocity measurements from SN Ia spectra have the potential to diminish systematic errors from the confounding of intrinsic colors and dust reddening affecting supernova distances. [ABSTRACT FROM AUTHOR]

We present a study of the spatial and color distributions of four early-type galaxies and their globular cluster (GC) systems observed as part of our ongoing wide-field imaging survey. We use BVR KPNO 4 m+MOSAIC imaging data to characterize the galaxies' GC populations, perform surface photometry of the galaxies, and compare the projected two-dimensional shape of the host galaxy light to that of the GC population. The GC systems of the ellipticals NGC 4406 and NGC 5813 both show an elliptical distribution consistent with that of the host galaxy light. Our analysis suggests a similar result for the giant elliptical NGC 4472, but a smaller GC candidate sample precludes a definite conclusion. For the S0 galaxy NGC 4594, the GCs have a circular projected distribution, in contrast to the host galaxy light, which is flattened in the inner regions. For NGC 4406 and NGC 5813, we also examine the projected shapes of the metal-poor and metal-rich GC subpopulations and find that both subpopulations have elliptical shapes that are consistent with those of the host galaxy light. Lastly, we use integrated colors and color profiles to compare the stellar populations of the galaxies to their GC systems. For each galaxy, we explore the possibility of color gradients in the individual metal-rich and metal-poor GC subpopulations. We find statistically significant color gradients in both GC subpopulations of NGC 4594 over the inner ∼5 effective radii (∼20 kpc). We compare our results to scenarios for the formation and evolution of giant galaxies and their GC systems. [ABSTRACT FROM AUTHOR]

We present details of the construction and characterization of the coaddition of the Sloan Digital Sky Survey (SDSS) Stripe 82 ugriz imaging data. This survey consists of 275 deg2 of repeated scanning by the SDSS camera over –50° ⩽ α ⩽ 60° and –1.°25 ⩽ δ ⩽ +1.°25 centered on the Celestial Equator. Each piece of sky has ∼20 runs contributing and thus reaches ∼2 mag fainter than the SDSS single pass data, i.e., to r ∼ 23.5 for galaxies. We discuss the image processing of the coaddition, the modeling of the point-spread function (PSF), the calibration, and the production of standard SDSS catalogs. The data have an r-band median seeing of 1.″1 and are calibrated to ⩽1%. Star color-color, number counts, and PSF size versus modeled size plots show that the modeling of the PSF is good enough for precision five-band photometry. Structure in the PSF model versus magnitude plot indicates minor PSF modeling errors, leading to misclassification of stars as galaxies, as verified using VVDS spectroscopy. There are a variety of uses for this wide-angle deep imaging data, including galactic structure, photometric redshift computation, cluster finding and cross wavelength measurements, weak lensing cluster mass calibrations, and cosmic shear measurements. [ABSTRACT FROM AUTHOR]

As brown dwarfs cool, a variety of species condense in their atmospheres, forming clouds. Iron and silicate clouds shape the emergent spectra of L dwarfs, but these clouds dissipate at the L/T transition. A variety of other condensates are expected to form in cooler T dwarf atmospheres. These include Cr, MnS, Na2S, ZnS, and KCl, but the opacity of these optically thinner clouds has not been included in previous atmosphere models. Here, we examine their effect on model T and Y dwarf atmospheres. The cloud structures and opacities are calculated using the Ackerman & Marley cloud model, which is coupled to an atmosphere model to produce atmospheric pressure-temperature profiles in radiative-convective equilibrium. We generate a suite of models between Teff = 400 and 1300 K, log g = 4.0 and 5.5, and condensate sedimentation efficiencies from fsed = 2 to 5. Model spectra are compared to two red T dwarfs, Ross 458C and UGPS 0722-05; models that include clouds are found to match observed spectra significantly better than cloudless models. The emergence of sulfide clouds in cool atmospheres, particularly Na2S, may be a more natural explanation for the “cloudy” spectra of these objects, rather than the reemergence of silicate clouds that wane at the L-to-T transition. We find that sulfide clouds provide a mechanism to match the near- and mid-infrared colors of observed T dwarfs. Our results indicate that including the opacity of condensates in T dwarf atmospheres is necessary to accurately determine the physical characteristics of many of the observed objects. [ABSTRACT FROM AUTHOR]

We study the mid-infrared color space of 30 galaxies from the Spitzer Infrared Nearby Galaxies Survey (SINGS) survey for which Sloan Digital Sky Survey data are also available. We construct two-color maps for each galaxy and compare them to results obtained from combining Maraston evolutionary synthesis models, galactic thermally pulsating asymptotic giant branch (TP-AGB) colors, and smooth star formation histories. For most of the SINGS sample, the spatially extended mid-IR emission seen by Spitzer in normal galaxies is consistent with our simple model in which circumstellar dust from TP-AGB stars dominates at 8 and 24 μm. There is a handful of exceptions that we identify as galaxies that have high star formation rates presumably with star formation histories that cannot be assumed to be smooth, or anemic galaxies, which were depleted of their H I at some point during their evolution and have very low ongoing star formation rates. [ABSTRACT FROM AUTHOR]

We investigate how star-forming galaxies typically assemble their masses at high redshift. Taking advantage of the deep multi-wavelength coverage of the GOODS data set, we select two of the largest samples of high-redshift star-forming galaxies based on their UV colors and measure stellar mass of individual galaxies. We use template-fitting photometry to obtain optimal estimates of the fluxes in lower-resolution ground-based and Spitzer images using prior information about galaxy positions, shapes, and orientations. By combining the data and realistic simulations to understand measurement errors and biases, we make a statistically robust determination of stellar mass function (SMF) of the UV-selected star-forming galaxies at z ∼ 4 and 5. We report a broad correlation between stellar mass and UV luminosity, such that more UV-luminous galaxies are, on average, also more massive. However, we show that the correlation has a substantial intrinsic scatter, particularly for UV-faint galaxies, evidenced by the fact there is a non-negligible number of UV faint but massive galaxies. Furthermore, we find that the low-mass end of the SMF does not rise as steeply as the UV luminosity function (αUVLF ≈ – (1.7-1.8) while αSMF ≈ – (1.3-1.4)) of the same galaxies. In a smooth and continuous formation scenario where star formation rates (SFRs) are sustained at the observed rates for a long time, these galaxies would have accumulated more stellar mass (by a factor of ≈3) than observed and therefore the SMF would mirror more closely that of the UV luminosity function. The relatively shallow slope of the SMF is due to the fact that many of the UV-selected galaxies are not massive enough, and therefore are too faint in their rest-frame optical bands, to be detected in the current observations. Our results favor a more episodic formation history in which SFRs of low-mass galaxies vary significantly over cosmic time, a scenario currently favored by galaxy clustering. Our findings for the UV-faint galaxies at high redshift are in contrast with previous studies on more UV-luminous galaxies, which exhibit a tighter SFR-Mstar correlation. The discrepancy may suggest that galaxies at different luminosities may have different evolutionary paths. Such a scenario presents a nontrivial test to theoretical models of galaxy formation. [ABSTRACT FROM AUTHOR]

We use Wide-field Infrared Survey Explorer (WISE) data covering the entire region (∼130 deg2) of the A2199 supercluster at z = 0.03 to study the mid-infrared (MIR) properties of supercluster galaxies. We identify an “MIR star-forming sequence” in the WISE [3.4]-[12] color-12 μm luminosity diagram, consisting of late-type, star-forming galaxies. At a fixed star formation rate, the MIR-detected galaxies at 22 μm or 12 μm tend to be more metal-rich and to have higher surface brightness than those without MIR detection. Using these MIR-detected galaxies, we construct the IR luminosity function (LF) and investigate its environmental dependence. Both total IR (TIR) and 12 μm LFs are dominated by late-type, star-forming galaxies. The contribution of active galactic nucleus host galaxies increases with both TIR and 12 μm luminosities. The contribution of early-type galaxies to the 12 μm LFs increases with decreasing luminosity. The faint-end slope of the TIR LFs does not change with environment, but the change of faint-end slope in the 12 μm LFs with the environment is significant: there is a steeper faint-end slope in the cluster core than in the cluster outskirts. This steepening results primarily from the increasing contribution of early-type galaxies toward the cluster. These galaxies are passively evolving, and contain old stellar populations with weak MIR emission from the circumstellar dust around asymptotic giant branch stars. [ABSTRACT FROM AUTHOR]

Photometric data in the UBV(RI)C system have been acquired for 80 solar analog stars for which we have previously derived highly precise atmospheric parameters Teff, log g, and [Fe/H] using high-resolution, high signal-to-noise ratio spectra. UBV and (RI)C data for 46 and 76 of these stars, respectively, are published for the first time. Combining our data with those from the literature, colors in the UBV(RI)C system, with ≃ 0.01 mag precision, are now available for 112 solar analogs. Multiple linear regression is used to derive the solar colors from these photometric data and the spectroscopically derived Teff, log g, and [Fe/H] values. To minimize the impact of systematic errors in the model-dependent atmospheric parameters, we use only the data for the 10 stars that most closely resemble our Sun, i.e., the solar twins, and derive the following solar colors: (B – V)☼ = 0.653 ± 0.005, (U – B)☼ = 0.166 ± 0.022, (V – R)☼ = 0.352 ± 0.007, and (V – I)☼ = 0.702 ± 0.010. These colors are consistent, within the 1σ errors, with those derived using the entire sample of 112 solar analogs. We also derive the solar colors using the relation between spectral-line-depth ratios and observed stellar colors, i.e., with a completely model-independent approach, and without restricting the analysis to solar twins. We find (B – V)☼ = 0.653 ± 0.003, (U – B)☼ = 0.158 ± 0.009, (V – R)☼ = 0.356 ± 0.003, and (V – I)☼ = 0.701 ± 0.003, in excellent agreement with the model-dependent analysis. [ABSTRACT FROM AUTHOR]

We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf satellite Ursa Major II (UMa II), spanning the magnitude range from V ∼ 15 to V ∼ 23.5 mag and extending over an 18 × 18 arcmin2 area centered on the Galaxy. Our photometry goes down to about 2 mag below the Galaxy's main-sequence turnoff that we detected at V ∼ 21.5 mag. We have discovered a bona fide RR Lyrae variable star in UMa II, which we use to estimate a conservative dereddened distance modulus for the galaxy of (m – M)0 = 17.70 ± 0.04 ± 0.12 mag, where the first error accounts for the uncertainties of the calibrated photometry, and the second reflects our lack of information on the metallicity of the star. The corresponding distance to UMa II is 34.7+0.6–0.7(+2.0–1.9) kpc. Our photometry shows evidence of a spread in the Galaxy's subgiant branch, compatible with a spread in metal abundance in the range between Z = 0.0001 and Z = 0.001. Based on our estimate of the distance, a comparison of the fiducial lines of the Galactic globular clusters M68 and M5 ([Fe/H] = –2.27 ± 0.04 dex and –1.33 ± 0.02 dex, respectively), with the position on the CMD of spectroscopically confirmed Galaxy members, may suggest the existence of stellar populations of different metal abundance/age in the central region of UMa II. [ABSTRACT FROM AUTHOR]

The Infrared Array Camera (IRAC) on the Spitzer Space Telescope has revealed that a number of high-mass protostars are associated with extended mid-infrared emission, particularly prominent at 4.5 μm. These are called “Green Fuzzy” emission or “Extended Green Objects.” We present color analysis of this emission toward six nearby (d = 2-3 kpc) well-studied high-mass protostars and three candidate high-mass protostars identified with the Spitzer GLIMPSE survey. In our color-color diagrams, most of the sources show a positive correlation between the [3.6]–[4.5] and [3.5]–[5.8] colors along the extinction vector in all or part of the region. We compare the colors with those of scattered continuum associated with the low-mass protostar L 1527, modeled scattered continuum in cavities, shocked emission associated with low-mass protostars, modeled H2 emission for thermal and fluorescent cases, and modeled polycyclic aromatic hydrocarbon (PAH) emission. Of the emission mechanisms discussed above, scattered continuum provides the simplest explanation for the observed linear correlation. In this case, the color variation within each object is attributed to different foreground extinctions at different positions. Alternative possible emission mechanisms to explain this correlation may be a combination of thermal and fluorescent H2 emission in shocks, and a combination of scattered continuum and thermal H2 emission, but detailed models or spectroscopic follow-up are required to investigate this possibility further. Our color-color diagrams also show possible contributions from PAHs in two objects. However, none of our samples show clear evidence for PAH emission directly associated with the high-mass protostars, several of which should be associated with ionizing radiation. This suggests that these protostars are heavily embedded even at mid-infrared wavelengths. [ABSTRACT FROM AUTHOR]