Shape Of Spectral Energy Distribution Research Articles

Infrared properties of active OB stars in the Magellanic Clouds from the Spitzer SAGE survey

AbstractWe present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs.

ASPITZERSURVEY OF PROTOPLANETARY DISK DUST IN THE YOUNG SERPENS CLOUD: HOW DO DUST CHARACTERISTICS EVOLVE WITH TIME?

We present Spitzer IRS mid-infrared (5-35 micron) spectra of a complete flux-limited sample (> 3 mJy at 8 micron) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and classified. Background stars (with slope consistent with a reddened stellar spectrum and silicate features in absorption), galaxies (with redshifted PAH features) and a planetary nebula (with high ionization lines) amount to 22% of contamination in this sample, leaving 115 true YSOs. Sources with rising spectra and ice absorption features, classified as embedded Stage I protostars, amount to 18% of the sample. The remaining 82% (94) of the disk sources are analyzed in terms of spectral energy distribution shapes, PAHs and silicate features. The presence, strength and shape of these silicate features are used to infer disk properties for these systems. About 8% of the disks have 30/13 micron flux ratios consistent with cold disks with inner holes or gaps, and 3% of the disks show PAH emission. Comparison with models indicates that dust grains in the surface of these disks have sizes of at least a few \mu\m. The 20 micron silicate feature is sometimes seen in absence of the 10 micron feature, which may be indicative of very small holes in these disks. No significant difference is found in the distribution of silicate feature shapes and strengths between sources in clusters and in the field. Moreover, the results in Serpens are compared with other well-studied samples: the c2d IRS sample distributed over 5 clouds and a large sample of disks in the Taurus star-forming region. The remarkably similar distributions of silicate feature characteristics in samples with different environment and median ages - if significant - imply that the dust population in the disk surface results from an equilibrium between dust growth and destructive collision processes that are maintained over a few million years for any YSO population irrespective of environment.

DUST PRODUCTION AND MASS LOSS IN THE GALACTIC GLOBULAR CLUSTER NGC 362

We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Due to its close proximity to the Small Magellanic Cloud (SMC), NGC 362 was imaged with the IRAC and MIPS cameras onboard the Spitzer Space Telescope as part of the Surveying the Agents of Galaxy Evolution (SAGE-SMC) Spitzer Legacy program. We detect several cluster members near the tip of the Red Giant Branch that exhibit infrared excesses indicative of circumstellar dust and find that dust is not present in measurable quantities in stars below the tip of the Red Giant Branch. We modeled the spectral energy distribution (SED) of the stars with the strongest IR excess and find a total cluster dust mass-loss rate of 3.0(+2.0/-1.2) x 10^-9 solar masses per year, corresponding to a gas mass-loss rate of 8.6(+5.6/-3.4) x 10^-6 solar masses per year, assuming [Fe/H] = -1.16. This mass loss is in addition to any dust-less mass loss that is certainly occurring within the cluster. The two most extreme stars, variables V2 and V16, contribute up to 45% of the total cluster dust-traced mass loss. The SEDs of the more moderate stars indicate the presence of silicate dust, as expected for low-mass, low-metallicity stars. Surprisingly, the SED shapes of the stars with the strongest mass-loss rates appear to require the presence of amorphous carbon dust, possibly in combination with silicate dust, despite their oxygen-rich nature. These results corroborate our previous findings in omega Centauri.

SPITZERSAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD

We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24 μm in the UBVIJHKs +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ~900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L ☉ ≥ 4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.

SPITZEROBSERVATIONS OF A GRAVITATIONALLY LENSED QUASAR, QSO 2237+0305

The four-image gravitationally lensed quasar QSO 2237+0305 is microlensed by stars in the lens galaxy. The amplitude of microlensing variability can be used to infer the relative size of the quasar as a function of wavelength; this provides a test of quasar models. Toward this end, we present Spitzer Space Telescope Infrared Spectrograph and Infrared Array Camera (IRAC) observations of QSO 2237+0305, finding the following. (1) The infrared (IR) spectral energy distribution (SED) is similar to that of other bright radio-quiet quasars, contrary to an earlier claim. (2) A dusty torus model with a small opening angle fits the overall shape of the IR SED well, but the quantitative agreement is poor due to an offset in wavelength of the silicate feature. (3) The flux ratios of the four lensed images can be derived from the IRAC data despite being unresolved. We find that the near-IR fluxes are increasingly affected by microlensing toward shorter wavelengths. (4) The wavelength dependence of the IRAC flux ratios is consistent with the standard quasar model in which an accretion disk and a dusty torus both contribute near 1 μm in the rest frame. This is also consistent with recent IR spectropolarimetry of nearby quasars.

HIGH-REDSHIFT DUST OBSCURED GALAXIES: A MORPHOLOGY-SPECTRAL ENERGY DISTRIBUTION CONNECTION REVEALED BY KECK ADAPTIVE OPTICS

A simple optical to mid-IR color selection, R – [24]>14, i.e., f_ν(24 μm)/f_ν(R) ≳ 1000, identifies highly dust obscured galaxies (DOGs) with typical redshifts of z ~ 2 ± 0.5. Extreme mid-IR luminosities (L_(IR) > 10^(12-14)) suggest that DOGs are powered by a combination of active galactic nuclei (AGNs) and star formation, possibly driven by mergers. In an effort to compare their photometric properties with their rest-frame optical morphologies, we obtained high-spatial resolution (0.05-0.1) Keck Adaptive Optics K'-band images of 15 DOGs. The images reveal a wide range of morphologies, including small exponential disks (eight of 15), small ellipticals (four of 15), and unresolved sources (two of 15). One particularly diffuse source could not be classified because of low signal-to-noise ratio. We find a statistically significant correlation between galaxy concentration and mid-IR luminosity, with the most luminous DOGs exhibiting higher concentration and smaller physical size. DOGs with high concentration also tend to have spectral energy distributions (SEDs) suggestive of AGN activity. Thus, central AGN light may be biasing the morphologies of the more luminous DOGs to higher concentration. Conversely, more diffuse DOGs tend to show an SED shape suggestive of star formation. Two of 15 in the sample show multiple resolved components with separations of ~1 kpc, circumstantial evidence for ongoing mergers.

The Nature of FaintSpitzer‐selected Dust‐obscured Galaxies

We use deep far-IR, submillimeter, radio, and X-ray imaging and mid-IR spectroscopy to explore the nature of a sample of Spitzer-selected dust-obscured galaxies (DOGs) in GOODS-N. A sample of 79 galaxies satisfy the criteria R − [ 24] > 14 (Vega) down to S_(24) > 100 μJy (median flux density S_(24) = 180 μJy). Twelve of these galaxies have IRS spectra available, which we use to measure redshifts and classify these objects as being dominated by star formation or active galactic nucleus (AGN) activity in the mid-IR. The IRS spectra and Spitzer photometric redshifts confirm that the DOGs lie in a tight redshift distribution around z ~ 2. Based on mid-IR colors, 80% of DOGs are likely dominated by star formation; the stacked X-ray emission from this subsample of DOGs is also consistent with star formation. Since only a small number of DOGs are individually detected at far-IR and submillimeter wavelengths, we use a stacking analysis to determine the average flux from these objects and plot a composite IR (8-1000 μm) spectral energy distribution (SED). The average luminosity of these star-forming DOGs is L_(IR) ~ 1 × 10^(12)L☉. We compare the average star-forming DOG to the average bright (S_(850) > 5 mJy) submillimeter galaxy (SMG); the S_(24) > 100 μJy DOGs are 3 times more numerous but 8 times less luminous in the IR. The far-IR SED shape of DOGs is similar to that of SMGs (average dust temperature of around 30 K), but DOGs have a higher mid-IR-to-far-IR flux ratio. The average star formation-dominated DOG has a star formation rate of 200 M☉ yr^(−1), which, given their space density, amounts to a contribution of 0.01 M☉yr^(−1) Mpc^(−3) (or 5%-10%) to the star formation rate density at z ~ 2.

Testing the blazar spectral sequence: X-ray-selected blazars

We present simultaneous optical and X-ray data from Swift for a sample of radio-loud flat-spectrum quasars selected from the Einstein Medium Sensitivity Survey (EMSS). We present also a complete analysis of Swift and INTEGRAL data on four blazars recently discussed as possibly challenging the trends of the hypothesized ‘blazar spectral sequence’. The spectral energy distributions (SEDs) of all these objects are modelled in terms of a general theoretical scheme, applicable to all blazars, leading to an estimate of the jets’ physical parameters. Our results show that, in the case of the EMSS broad line blazars, X-ray selection does not lead to find sources with synchrotron peaks in the UV/X-ray range, as was the case for X-ray-selected BL Lacs. Instead, for a wide range of radio powers all the sources with broad emission lines show similar SEDs, with synchrotron components peaking below the optical/UV range. The SED models suggest that the associated inverse Compton (IC) emission should peak below the GeV range, but could be detectable in some cases by the Fermi Gamma-ray Space Telescope. Of the remaining four ‘anomalous’ blazars, two highly luminous sources with broad lines, claimed to possibly emit synchrotron X-rays, are shown to be better described with IC models for their X-ray emission. For one source with weak emission lines (a BL Lac object) a synchrotron peak in the soft X-ray range is confirmed, while for the fourth source, exhibiting narrow emission lines typical of narrow-line Seyfert 1 galaxies, no evidence of X-ray emission from a relativistic jet is found. We re-examine the standing and interpretation of the original ‘blazar spectral sequence’ and suggest that the photon ambient, in which the particle acceleration and emission occur, is likely the main factor determining the shape of the blazar SED. A connection between SED shape and jet power/luminosity can however result through the link between the mass and accretion rate of the central black hole and the radiative efficiency of the resulting accretion flow, thus involving at least two parameters.

Infrared Spectral Energy Distributions ofz∼ 0.7 Star‐forming Galaxies

We analyze the infrared (IR) spectral energy distributions (SEDs) for 10 μm < λrest < 100 μm for ~600 galaxies at z ~ 0.7 in the extended Chandra Deep Field South by stacking their Spitzer 24, 70, and 160 μm images. We place interesting constraints on the average IR SED shape in two bins: the brightest 25% of z ~ 0.7 galaxies detected at 24 μm, and the remaining 75% of individually detected galaxies. Galaxies without individual detections at 24 μm were not well detected at 70 and 160 μm even through stacking. We find that the average IR SEDs of z ~ 0.7 star-forming galaxies fall within the diversity of z ~ 0 templates. While dust obscuration LIR/LUV seems to be only a function of star formation rate (SFR; ~LIR + LUV), not of redshift, the dust temperature of star-forming galaxies (with SFR ~ 10 M☉ yr-1 ) at a given IR luminosity was lower at z ~ 0.7 than today. We suggest an interpretation of this phenomenology in terms of dust geometry: intensely star-forming galaxies at z ~ 0 are typically interacting, and host dense centrally concentrated bursts of star formation and warm dust temperatures. At z ~ 0.7, the bulk of intensely star-forming galaxies are relatively undisturbed spirals and irregulars, and we postulate that they have large amounts of widespread lower density star formation, yielding lower dust temperatures for a given IR luminosity. We recommend which IR SEDs are most suitable for modeling intermediate-redshift galaxies with different SFRs.

The use of genetic algorithms to model protoplanetary discs

The protoplanetary discs of T Tauri and Herbig Ae/Be stars have previously been studied using geometric disc models to fit their spectral energy distribution (SED). The simulations provide a means to reproduce the signatures of various circumstellar structures, which are related to different levels of infrared excess. With the aim of improving our previous model, which assumed a simple flat-disc configuration, we adopt here a reprocessing flared-disc model that assumes hydrostatic, radiative equilibrium. We have developed a method to optimize the parameter estimation based on genetic algorithms (GAs). This paper describes the implementation of the new code, which has been applied to Herbig stars from the Pico dos Dias Survey catalogue, in order to illustrate the quality of the fitting for a variety of SED shapes. The star AB Aur was used as a test of the GA parameter estimation, and demonstrates that the new code reproduces successfully a canonical example of the flared-disc model. The GA method gives a good quality of fit, but the range of input parameters must be chosen with caution, as unrealistic disc parameters can be derived. It is confirmed that the flared-disc model fits the flattened SEDs typical of Herbig stars; however, embedded objects (increasing SED slope) and debris discs (steeply decreasing SED slope) are not well fitted with this configuration. Even considering the limitation of the derived parameters, the automatic process of SED fitting provides an interesting tool for the statistical analysis of the circumstellar luminosity of large samples of young stars.

The ISOPHOT - MAMBO survey of 3CR radio sources: Further evidence for the unified schemes

We present the complete set of ISOPHOT observations of 3CR radio galaxies and quasars, which are contained in the ISO Data Archive, providing 75 mid- and far-infrared spectral energy distributions (SEDs) between 5 and 200µm. For 28 sources they are supplemented with MAMBO 1.2 mm observations and for 15 sources with new submillimetre data from the SCUBA archive. The sample includes flat and steep spectru m quasars, broad and narrow line radio galaxies, as well as Fanaroff-Riley FR 1 and FR 2 types. The SED shapes exhibit a diversity in the infrared (IR), ranging from a smooth dominating synchrotron component in flat spectrum sources to a thermal d ust bump around 60-100 µm in steep spectrum sources. The detection rate of a thermal bump in more than 50% of the cases suggests that dust emission may be a general phenomenon in these sources. We check the orientation-dependent unifie d scheme, in which the powerful FR 2 narrow line galaxies are quasars viewed at high inclination, so that their nuclei are hidden behind a dust torus intercepting the optical-ultrav iolet AGN radiation and reemitting it in the infrared. We find that (1) b oth the quasars and the galaxies show a high mid- to far-infrared luminosity ratio typical for powerful AGNs and (2) - when matched in 178 MHz luminosity - both show the same ratio of isotropic far-infrared to isotropic 178 MHz lobe power. Therefore, from our large sample investigated here we find stron g evidence for the orientation-dependent unification of the p owerful FR 2 galaxies with the quasars. The distribution of the dust- to-lobe luminosity ratio shows a dispersion which we suggest to be most likely due to the additional influence of evolutio n and environment superposed on the orientation-dependent unification. We discuss our data also in the frame of the recedi ng torus model. At the high 178 MHz luminosities of our sources above 10 26.5 W/Hz we do not find any support for this model in its original formulation and therefore we propose a refine ment: The scale height of the torus might not be independent of luminosity, rather it may increase at high luminosities due to the impact of supernovae from starbursts accompanying the AGN phenomena.

Indications for Grain Growth and Mass Decrease in Cold Dust Disks around Classical T Tauri Stars in the MBM 12 Young Association

We report the detection of continuum emission at λ = 850 and 450 μm from disks around four classical T Tauri stars in the MBM 12 (L1457) young association. Using a simple model, we infer masses of 0.0014-0.012 M☉ for the disk of LkHα 263 ABC, 0.005-0.021 M☉ for S18 ABab, 0.03-0.18 M☉ for LkHα 264 A, and 0.023-0.23 M☉ for LkHα 262. The disk mass found for LkHα 263 ABC is consistent with the 0.0018 M☉ inferred from the scattered-light image of the edge-on disk around component C. Comparison to earlier 13CO line observations indicates CO depletion by up to a factor of 300 with respect to dark-cloud values. The spectral energy distributions (SEDs) suggest grain growth, possibly to sizes of a few hundred microns, but our spatially unresolved data cannot rule out opacity as an explanation for the SED shape. Our observations show that these T Tauri stars are still surrounded by significant reservoirs of cold material at an age of 1-5 Myr. We conclude that the observed differences in disk mass are likely explained by binary separation affecting the initial value. With available accretion rate estimates we find that our data are consistent with theoretical expectations for viscously evolving disks having decreased their masses by ~30%.

A multi-wavelength test of the FR I–BL Lac unifying model

We collect multi-wavelength measurements of the nuclear emission of 20 low luminosity FR I radio-galaxies to test the viability of the FR I - BL Lac unifying model. Although poorly sampled, the Spectral Energy Distributions (SED) of FR Is are consistent with the double peaked shape characteristic of BL Lacs. Furthermore while the distribution of the FR Is in the broad-band spectral index planes shows essentially no overlap with the regions where HBL and LBL are located, this can be simply due to the effects of relativistic beaming. More quantitatively, deriving the beaming Doppler factor of a given radio-galaxy from its X-ray luminosity ratio with respect to BL Lacs with similar extended radio luminosity, we find that i) the luminosity in all bands, ii) the value of the spectral indices, iii) the slope of the X-ray spectrum, iv) the overall SED shape, may be all simultaneously reproduced. However, the corresponding jet bulk Lorentz factors are significantly smaller than those derived for BL Lacs from other observational and theoretical considerations. This suggests to consider a simple variant of the unification scheme that allows for the presence of a velocity structure in the jet.

Infrared to millimetre photometry of ultra-luminous IR galaxies : New evidence favouring a 3-stage dust model

Infrared to millimetre spectral energy distributions (SEDs) have been obtained for 41 bright ultra- luminous infrared galaxies (ULIRGs). The observations were carried out with ISOPHOT between 10 and 200 m and supplemented for 16 sources with JCMT/SCUBA at 450 and 850 m and with SEST at 1.3 mm. In addition, seven sources were observed at 1.2 and 2.2 m with the 2.2 m telescope on Calar Alto. These new SEDs represent the most complete set of infrared photometric templates obtained so far on ULIRGs in the local universe. The SEDs peak at 60{100 m and show often a quite shallow Rayleigh-Jeans tail. Fits with one single modied blackbody yield a high FIR opacity and small dust emissivity exponent T >30 K) to cold (30 K >T >10 K) temperatures. This provides evidence for two dust stages, the cool starburst dominated one and the cold cirrus-like one. The third stage with several hundred Kelvin warm dust is identied in the AGN dominated ULIRGs, showing up as a NIR-MIR power- law flux increase. While AGNs and SBs appear indistinguishable at FIR and submm wavelengths, they dier in the NIR-MIR. This suggests that the cool FIR emitting dust is not related to the AGN, and that the AGN only powers the warm and hot dust. In comparison with optical and MIR spectroscopy, a criterion based on the SED shapes and the NIR colours is established to reveal AGNs among ULIRGs. Also the possibility of recognising evolutionary trends among the ULIRGs via the relative amounts of cold, cool and warm dust components is investigated.

The effective temperatures of carbon-rich stars

We evaluate effective temperatures of 390 carbon-rich stars. The interstellar extinction on their lines of sights was determined and circumstellar contributions derived. The intrinsic (dereddened) spectral energy distributions (SEDs) are classified into 14 photometric groups (HCi , CVj and SCV with ,5 and ,7). The new scale of effective temperatures proposed here is calibrated on the 54 angular diameters (measured on 52 stars) available at present from lunar occultations and interferometry. The brightness distribution on stellar discs and its influence on diameter evaluations are discussed. The effective temperatures directly deduced from those diameters correlate with the classification into photometric groups, despite the large error bars on diameters. The main parameter of our photometric classification is thus effective temperature . Our photometric coefficients are shown to be angular diameters on a relative scale for a given photometric group, (more precisely for a given effective temperature). The angular diameters are consistent with the photometric data previously shown to be consistent with the true parallaxes from HIPPARCOS observations (Knapik, et al. [CITE], Sect. 6). Provisional effective temperatures, as constrained by a successful comparison of dereddened SEDs from observations to model atmosphere predictions, are in good agreement with the values directly calculated from the observed angular diameters and with those deduced from five selected intrinsic color indices. These three approaches were used to calibrate a reference angular diameter and the associated coefficient . The effective temperature proposed for each star is the arithmetic mean of two estimates, one (bolometric) from a reference integrated flux F 0 , the other (spectral) from calibrated color indices which are representative of SED shapes. Effective temperatures for about 390 carbon stars are provided on this new homogeneous scale, together with values for some stars classified with oxygen-type SEDs with a total of 438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given. Objects with strong infrared excesses and optically thick circumstellar dust shells are discussed separately. The new effective temperature scale is shown to be compatible and (statistically) consistent with the sample of direct values from the observed angular diameters. The effective temperatures are confirmed to be higher than the mean color temperatures (from 140 to 440 K). They are in good agreement with the published estimates from the infrared flux method for , while an increasing discrepancy is observed toward lower temperatures. As an illustration of the efficiency of the photometric classification and effective temperature scale, the C/O ratios and the Merrill-Sanford (M-S) band intensities are investigated. It is shown that the maximum value, mean value and dispersion of C/O increase along the photometric CV-sequence, i.e. with decreasing effective temperature. The M-S bands of are shown to have a transition from noneto strongat . Simultaneously, with decreasing effective temperature, the mean C/O ratio increases from 1.04 to 1.36, the transition in strength occurring while .

Multiwavelength properties of blazars

Blazar spectral energy distributions (SEDs) are double peaked and follow a self-similar sequence in luminosity. The so-called “blue” blazars, whose first SED component peaks at X-ray energies, are TeV sources, although with a relatively small fraction of their bolometric luminosities. The “red” blazars, with SED peaks in the infrared-optical range, appear to emit relatively more power in the gamma-ray component but at much lower energies (GeV and below). Correlated variations across the SEDs (of both types) are consistent with the picture that a single electron population gives rise to the high-energy parts of both SED components, via synchrotron at low energies and Compton-scattering at high energies. In this scenario, the trends of SED shape with luminosity can be explained by electron cooling on ambient photons. With simple assumptions, we can make some estimates of the physical conditions in blazar jets of each “type” and can predict which blazars are the most likely TeV sources. Upper limits from a mini-survey of candidate TeV sources indicate that only ∼ 10% of their bolometric luminosity is radiated in gamma-rays, assuming the two SED components peak near 1 keV and 1 TeV. Finally, present blazar samples are too shallow to indicate what kinds of jets nature prefers, i.e., whether the low-luminosity “blue” blazars or the high-luminosity “red” blazars are more common.

IRAS observations of young stellar objects in the Corona Australis dark cloud

The young stellar object (YSO) population associated with the dark cloud complex in Corona Australis is studied by synthesizing IRAS data with newly obtained near-IR and mid-IR photometry and previously published optical/IR data. Twenty-four YSOs in the Cr A complex are identified. The observed range of spectral energy distribution shapes and bolometric luminosities are consistent with those observed in other dark clouds. The duration and efficiency of star formation are found to be similar to the Rho Ophiuchi IR cluster. The low number of YSOs compared to other dark clouds is understood by a reevaluation of the molecular mass of the R Cr A cloud which shows it to be much less massive than previously assumed.

On spectral energy distribution shape of fluorescent lamp phosphors

Broad-band emission of representative lamp phosphors were compared with the Gauss error function. Deviation from the Gauss curve was observed in the high energy side of the emission peak for s 2 ion activators, and in the low energy side for Mn 2+ and Eu 2+. In the former group, the deviation is attributed to the weak subbands. In the latter, the configurational coordinate model with small Stokes shift accounts for the asymmetry.