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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,189 records · Page 66
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DOE OSTI2015

Massive young stellar object W42-MME: The discovery of an infrared jet using VLT/NACO near-infrared images

We report on the discovery of an infrared jet from a deeply embedded infrared counterpart of the 6.7 GHz methanol maser emission (MME) in W42 (i.e., W42-MME). We show that W42-MME drives a parsec-scale H{sub 2} outflow, with the detection of a bow shock feature at ∼0.52 pc to the north. The inner ∼0.4 pc part of the H{sub 2} outflow has a position angle of ∼18° and the position angle of ∼40° is found farther away on either side of the outflow from W42-MME. W42-MME is detected at wavelengths longer than 2.2 μm and is a massive young stellar object with an estimated stellar mass of 19 ± 4 M{sub ⊙}. We map the inner circumstellar environment of W42-MME using Very Large Telescope (VLT)/NACO adaptive optics K{sub s} and L′ observations at resolutions of ∼0.″ 2 and ∼0.″1, respectively. We discover a collimated jet in the inner 4500 AU using the L′ band, which contains prominent Brα line emission. The jet is located inside an envelope/cavity (extent ∼10,640 AU) that is tapered at both ends and is oriented along the north–south direction. Such observed morphology of the outflow cavity around the massive star is scarcely known and is very crucial for understanding the jet-outflow formation process in massive star formation. Along the flow axis, which is parallel to the previously known magnetic field, two blobs are found in both the NACO images at distances of ∼11800 AU, located symmetrically from W42-MME. The observed W42-MME jet-outflow configuration can be used to constrain the jet launching and jet collimation models in massive star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

What are LITTLE WORLDS made of? Stellar abundances and the building blocks of planets

If the photospheres of solar-type stars represent the composition of circumstellar disks from which any planets formed, spectroscopic determinations of stellar elemental abundances offer information on the composition of those planets, including smaller, rocky planets. In particular, the C/O ratio is proposed to be a key determinant of the composition of solids that condense from disk gas and are incorporated into planets. Also, planets may leave chemical signatures on the photospheres of their host stars by sequestering heavy elements, or by being accreted by the stars. The presence, absence, and composition of planets could be revealed by small differences in the relative abundances between stars. I critically examine these scenarios and show that (i) a model of Galactic chemical evolution predicts that the C/O ratio is expected to be close to the solar value and varies little between dwarf stars in the solar neighborhood; (ii) spectroscopic surveys of M dwarf stars limit the occurrence of stars with C/O ≳ 1 to <10{sup −3}; and (iii) planetesimal chemistry will be controlled by the composition of oxygen-rich dust inherited from the molecular cloud and processed in a dust-rich environment, not a gas with the stellar composition. A second generation of more reduced planetesimals could be produced by re-equilibration of material with dust-depleted gas. Finally, I discuss how minor differences in relative abundances between stars that correlate with condensation temperature can be explained by dust-gas segregation, perhaps in circumstellar disks, rather than planet formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

DETECTING TRIAXIALITY IN THE GALACTIC DARK MATTER HALO THROUGH STELLAR KINEMATICS. II. DEPENDENCE ON NATURE DARK MATTER AND GRAVITY

Recent studies have presented evidence that the Milky Way global potential may be non-spherical. In this case, the assembling process of the Galaxy may have left long-lasting stellar halo kinematic fossils due to the shape of the dark matter halo, potentially originated by orbital resonances. We further investigate such a possibility, now considering potential models further away from ΛCDM halos, like scalar field dark matter halos and Modified Newtonian Dynamics (MOND), and including several other factors that may mimic the emergence and permanence of kinematic groups, such as a spherical and triaxial halo with an embedded disk potential. We find that regardless of the density profile (DM nature), kinematic groups only appear in the presence of a triaxial halo potential. For the case of a MOND-like gravity theory no kinematic structure is present. We conclude that the detection of these kinematic stellar groups could confirm the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

STRUCTURAL GLITCHES NEAR THE CORES OF RED GIANTS REVEALED BY OSCILLATIONS IN G-MODE PERIOD SPACINGS FROM STELLAR MODELS

With recent advances in asteroseismology it is now possible to peer into the cores of red giants, potentially providing a way to study processes such as nuclear burning and mixing through their imprint as sharp structural variations—glitches—in the stellar cores. Here we show how such core glitches can affect the oscillations we observe in red giants. We derive an analytical expression describing the expected frequency pattern in the presence of a glitch. This formulation also accounts for the coupling between acoustic and gravity waves. From an extensive set of canonical stellar models we find glitch-induced variation in the period spacing and inertia of non-radial modes during several phases of red giant evolution. Significant changes are seen in the appearance of mode amplitude and frequency patterns in asteroseismic diagrams such as the power spectrum and the échelle diagram. Interestingly, along the red giant branch glitch-induced variation occurs only at the luminosity bump, potentially providing a direct seismic indicator of stars in that particular evolution stage. Similarly, we find the variation at only certain post-helium-ignition evolution stages, namely, in the early phases of helium core burning and at the beginning of helium shell burning, signifying the asymptotic giant branch bump. Based on our results, we note that assuming stars to be glitch-free, while they are not, can result in an incorrect estimate of the period spacing. We further note that including diffusion and mixing beyond classical Schwarzschild could affect the characteristics of the glitches, potentially providing a way to study these physical processes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Linking galaxies to dark matter halos at z ∼ 1: Dependence of galaxy clustering on stellar mass and specific star formation rate

We study the dependence of angular two-point correlation functions on stellar mass (M{sub *}) and specific star formation rate (sSFR) of M{sub ∗}>10{sup 10}M{sub ⊙} galaxies at z∼1. The data from the UK Infrared Telescope Infrared Deep Sky Survey Deep eXtragalactic Survey and Canada–France–Hawaii Telescope Legacy Survey cover 8.2 deg{sup 2} sample scales larger than 100 h{sup −1} Mpc at z∼1, allowing us to investigate the correlation between clustering, M{sub *}, and star formation through halo modeling. Based on halo occupation distributions (HODs) of M{sub *} threshold samples, we derive HODs for M{sub *} binned galaxies, and then calculate the M{sub ∗}/M{sub halo} ratio. The ratio for central galaxies shows a peak at M{sub halo}∼10{sup 12}h{sup −1}M{sub ⊙}, and satellites predominantly contribute to the total stellar mass in cluster environments with M{sub ∗}/M{sub halo} values of 0.01–0.02. Using star-forming galaxies split by sSFR, we find that main sequence galaxies (log sSFR/yr{sup −1}∼−9) are mainly central galaxies in ∼10{sup 12.5}h{sup −1}M{sub ⊙} halos with the lowest clustering amplitude, while lower sSFR galaxies consist of a mixture of both central and satellite galaxies where those with the lowest M{sub *} are predominantly satellites influenced by their environment. Considering the lowest M{sub halo} samples in each M{sub *} bin, massive central galaxies reside in more massive halos with lower sSFRs than low mass ones, indicating star-forming central galaxies evolve from a low M{sub *}–high sSFR to a high M{sub *}–low sSFR regime. We also find that the most rapidly star-forming galaxies (log sSFR/yr{sup −1}>−8.5) are in more massive halos than main sequence ones, possibly implying galaxy mergers in dense environments are driving the active star formation. These results support the conclusion that the majority of star-forming galaxies follow secular evolution through the sustained but decreasing formation of stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Short-period stellar activity cycles with Kepler photometry

We study the short-periodic component of stellar activity with a cycle period of P{sub cyc}<10{sup 3} days using the Kepler mission photometry of fast-rotating (1<P<4 days) stars with spectra of M4V to F3V. Applying the originally developed two non-spectral methods, we measured the effective period of stellar cycles in 462 objects. The obtained results are in accordance with previous measurements by Vida et al. and do not seem to result from a beating effect. The performed measurements of P{sub cyc} cluster in a specific branch that covers the previously unstudied region in the Saar and Brandenburg diagram and connects the branch of inactive stars with the area populated by super-active objects. It is shown that the formation of the discovered branch is due to the α-quenching effect, which saturates the magnetic dynamo and decreases the cycle periods with the increase of the inverted Rossby number. This finding is important in the context of the discussion on catastrophic quenching and other heuristic approximations of the nonlinear α-effect.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The age and age spread of the Praesepe and Hyades clusters: A consistent, ∼800 Myr picture from rotating stellar models

We fit the upper main sequence of the Praesepe and Hyades open clusters using stellar models with and without rotation. When neglecting rotation, we find that no single isochrone can fit the entire upper main sequence at the clusters’ spectroscopic metallicity: more massive stars appear, at high significance, to be younger than less massive stars. This discrepancy is consistent with earlier studies, but vanishes when including stellar rotation. The entire upper main sequence of both clusters is very well-fit by a distribution of 800 Myr old stars with the spectroscopically measured [Fe/H] = 0.12. The increase over the consensus age of ∼600–650 Myr is due both to the revised solar metallicity (from Z{sub ⊙}≈0.02 to Z{sub ⊙}≈0.014) and to the lengthening of main-sequence lifetimes and increase in luminosities with rapid rotation. Our results show that rotation can remove the need for large age spreads in intermediate-age clusters, and that these clusters may be significantly older than is commonly accepted. A Hyades/Praesepe age of ∼800 Myr would also require a recalibration of rotation/activity age indicators.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Older and colder: The impact of starspots on pre-main-sequence stellar evolution

We assess the impact of starspots on the evolution of late-type stars during the pre-main sequence (pre-MS) using a modified stellar evolution code. We find that heavily spotted models of mass 0.1–1.2 M{sub ⊙} are inflated by up to 10% during the pre-MS, and up to 4% and 9% for fully and partially convective stars at the zero-age MS, consistent with measurements from active eclipsing binary systems. Spots similarly decrease stellar luminosity and T{sub eff}, causing isochrone-derived masses to be underestimated by up to a factor of 2×, and ages to be underestimated by a factor of 2–10, at 3 Myr. Consequently, pre-MS clusters and their active stars are systematically older and more massive than often reported. Cluster ages derived with the lithium depletion boundary technique are erroneously young by ∼15% and 10% at 30 and 100 Myr, respectively, if stars with 50% spots are interpreted with unspotted models. Finally, lithium depletion is suppressed in spotted stars with radiative cores, leading to a fixed-temperature lithium dispersion on the MS if a range of spot properties are present on the pre-MS. Such dispersions are large enough to explain Li abundance spreads seen in young open clusters, and imply a range of radii at fixed mass and age during the pre-MS Li-burning epoch. By extension, this implies that mass, composition, and age do not uniquely specify the Hertzsprung–Russell diagram location of pre-MS stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Cosmic history of the integrated galactic stellar initial mass function: A simulation study

Theoretical and indirect observational evidence suggests that the stellar initial mass function (IMF) increases with redshift. On the other hand, star formation rates (SFRs) may be as high as 100 M{sub ⊙} yr{sup −1} in starburst galaxies. These may lead to the formation of massive clusters, hence massive stars, making the integrated galactic stellar initial mass function (IGIMF) top-heavy (i.e., the proportion of massive stars is higher than that of less massive stars). We investigate the joint effect of evolving the IMF and several measures of SFRs in dependence on the galaxy-wide IMF. The resulting IGIMFs have slopes α{sub 2,IGIMF} in the high-mass regime, which is highly dependent on the minimum mass of the embedded cluster (M{sub ecl,min}), SFR, and mass-spectrum indices of embedded clusters (β). It is found that for z ∼ 0–2, α{sub 2,IGIMF} becomes steeper (i.e., bottom-heavy), for z ∼ 2–4, α{sub 2,IGIMF} becomes flatter (i.e., top-heavy ), and from z ∼ 4 onward, α{sub 2,IGIMF} again becomes steeper. The effects are faster for higher values of β. α{sub 2,IGIMF} is also for higher values of M{sub ecl,min}. All of these effects may be attributable to the joint effect of increasing the temperature of the ambient medium as well as varying the SFR with increasing redshift.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. III. A QUINTUPLE STELLAR POPULATION IN NGC 2808

In this study we present the first results from multi-wavelength Hubble Space Telescope (HST) observations of the Galactic globular cluster (GC) NGC 2808 as an extension of the Hubble Space Telescope UV Legacy Survey of Galactic GCs (GO-13297 and previous proprietary and HST archive data). Our analysis allowed us to disclose a multiple-stellar-population phenomenon in NGC 2808 even more complex than previously thought. We have separated at least five different populations along the main sequence and the red giant branch (RGB), which we name A, B, C, D, and E (though an even finer subdivision may be suggested by the data). We identified the RGB bump in four out of the five RGBs. To explore the origin of this complex color–magnitude diagram, we have combined our multi-wavelength HST photometry with synthetic spectra, generated by assuming different chemical compositions. The comparison of observed colors with synthetic spectra suggests that the five stellar populations have different contents of light elements and helium. Specifically, if we assume that NGC 2808 is homogeneous in [Fe/H] (as suggested by spectroscopy for Populations B, C, D, E, but lacking for Population A) and that population A has a primordial helium abundance, we find that populations B, C, D, E are enhanced in helium by ΔY ∼ 0.03, 0.03, 0.08, 0.13, respectively. We obtain similar results by comparing the magnitude of the RGB bumps with models. Planned spectroscopic observations will test whether Population A also has the same metallicity, or whether its photometric differences with Population B can be ascribed to small [Fe/H] and [O/H] differences rather than to helium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Mapping the outer edge of the young stellar cluster in the galactic center

We present new near-infrared spectroscopic observations of the outer edges of the young stellar cluster around the supermassive black hole at the Galactic center. The observations show a break in the surface density profile of young stars at ∼13″ (0.52 pc). These observations spectroscopically confirm previous suggestions of a break based on photometry. Using Gemini North's Near-Infrared Integral Field Spectrometer, we are able to detect and separate early- and late-type stars with a 75% completeness at K{sub s}=15.5. We sample a region with radii between 7″ and 23″ (0.28–0.92 pc) from Sgr A* and present new spectral classifications of 144 stars brighter than K{sub s}=15.5, where 140 stars are late-type (>1 Gyr) and only four stars are early-type (young, 4–6 Myr). A broken power-law fit of the early-type surface density matches well with our data and previously published values. The projected surface density of late-type stars is also measured and found to be consistent with previous results. We find that the observed early-type surface-density profile is inconsistent with the theory of young stars originating from a tightly bound infalling cluster, as no significant trail of young stars is found at radii above 13″. We also note that either a simple disk instability criterion or a cloud–cloud collision could explain the location of the outer edge, though we lack information to make conclusive remarks on either alternative. If this break in surface density represents an edge to the young stellar cluster, it would set an important scale for the most recent episode of star formation at the Galactic center.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

No evidence for multiple stellar populations in the low-mass galactic globular cluster E3

Multiple stellar populations are a widespread phenomenon among Galactic globular clusters. Even though the origin of the enriched material from which new generations of stars are produced remains unclear, it is likely that self-enrichment will be feasible only in clusters massive enough to retain this enriched material. We searched for multiple populations in the low mass (M∼1.4×10{sup 4} M{sub ⊙}) globular cluster E3, analyzing SOAR/Goodman multi-object spectroscopy centered on the blue cyanogen (CN) absorption features of 23 red giant branch stars. We find that the CN abundance does not present the typical bimodal behavior seen in clusters hosting multistellar populations, but rather a unimodal distribution that indicates the presence of a genuine single stellar population, or a level of enrichment much lower than in clusters that show evidence for two populations from high-resolution spectroscopy. E3 would be the first bona fide Galactic old globular cluster where no sign of self-enrichment is found.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE CLUSTERING OF RADIO GALAXIES: BIASING AND EVOLUTION VERSUS STELLAR MASS

We study the angular clustering of ∼6 × 10{sup 5} NVSS sources on scales ≳50h{sup −1} Mpc in the context of the ΛCDM scenario. The analysis partially relies on the redshift distribution of 131 radio galaxies, inferred from the Hercules and CENSORS survey, and an empirical fit to the stellar-to-halo mass relation. For redshifts z ≲ 0.7, the fraction of radio activity versus stellar mass evolves as f{sub R{sub L}}∼M{sub ∗}{sup α{sub 0}+α{sub 1}z}, where α{sub 0} = 2.529 ± 0.184 and α{sub 1}=1.854{sub −0.761}{sup +0.708}. The estimate on α{sub 0} is largely driven by the results of Best et al., while the constraint on α{sub 1} is new. We derive a biasing factor b(z=0.5)=2.093{sub −0.109}{sup +0.164} between radio galaxies and the underlying mass. The function b(z)=0.33z{sup 2}+0.85z+1.6 fits well the redshift dependence. We also provide convenient parametric forms for the redshift-dependent radio luminosity function, which are consistent with the redshift distribution and the NVSS source count versus flux.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

BEYOND THE MAIN SEQUENCE: TESTING THE ACCURACY OF STELLAR MASSES PREDICTED BY THE PARSEC EVOLUTIONARY TRACKS

Characterizing the physical properties of exoplanets and understanding their formation and orbital evolution requires precise and accurate knowledge of their host stars. Accurately measuring stellar masses is particularly important because they likely influence planet occurrence and the architectures of planetary systems. Single main-sequence stars typically have masses estimated from evolutionary tracks, which generally provide accurate results due to their extensive empirical calibration. However, the validity of this method for subgiants and giants has been called into question by recent studies, with suggestions that the masses of these evolved stars could have been overestimated. We investigate these concerns using a sample of 59 benchmark evolved stars with model-independent masses (from binary systems or asteroseismology) obtained from the literature. We find very good agreement between these benchmark masses and the ones estimated using evolutionary tracks. The average fractional difference in the mass interval ∼0.7–4.5 M{sub ⊙} is consistent with zero (−1.30 ± 2.42%), with no significant trends in the residuals relative to the input parameters. A good agreement between model-dependent and -independent radii (−4.81 ± 1.32%) and surface gravities (0.71 ± 0.51%) is also found. The consistency between independently determined ages for members of binary systems adds further support for the accuracy of the method employed to derive the stellar masses. Taken together, our results indicate that determination of masses of evolved stars using grids of evolutionary tracks is not significantly affected by systematic errors, and is thus valid for estimating the masses of isolated stars beyond the main sequence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Stellar velocity dispersion and anisotropy of the Milky Way inner halo

We measure the three components of velocity dispersion, σ{sub R}, σ{sub θ}, σ{sub ϕ}, for stars within 6 < R < 30 kpc of the Milky Way using a new radial velocity sample from the MMT telescope. We combine our measurements with previously published data so that we can more finely sample the stellar halo. We use a maximum likelihood statistical method for estimating mean velocities, dispersions, and covariances assuming only that velocities are normally distributed. The alignment of the velocity ellipsoid is consistent with a spherically symmetric gravitational potential. From the spherical Jeans equation, the mass of the Milky Way is M(R⩽12 kpc)=1.3×10{sup 11} M{sub ⊙} with an uncertainty of 40%. We also find a region of discontinuity, 15 ≲ R ≲ 25 kpc, where the estimated velocity dispersions and anisotropies diverge from their anticipated values, confirming the break observed by others. We argue that this break in anisotropy is physically explained by coherent stellar velocity structure in the halo, such as the Sgr stream. To significantly improve our understanding of halo kinematics will require combining radial velocities with future Gaia proper motions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Stellar and gas dynamical model for tidal disruption events in a quiescent galaxy

A detailed model of the tidal disruption events (TDEs) has been constructed using stellar dynamical and gas dynamical inputs that include black hole (BH) mass M{sub •}, specific orbital energy E and angular momentum J, star mass M{sub ⋆} and radius R{sub ⋆,} and the pericenter of the star orbit r{sub p}(E, J, M{sub •}). We solved the steady state Fokker–Planck equation using the standard loss cone theory for the galactic density profile ρ (r) ∝ r{sup −γ} and stellar mass function ξ(m) where m = M{sub ⋆}/M{sub ⊙} and obtained the feeding rate of stars to the BH integrated over the phase space as N-dot {sub t}∝M{sub ∙}{sup β}, where β=−0.3±0.01 for M{sub •} > 10{sup 7}M{sub ⊙} and ∼6.8 × 10{sup −5} Yr{sup −1} for γ = 0.7. We use this to model the in-fall rate of the disrupted debris, M-dot (E,J,m,t), and discuss the conditions for the disk formation, finding that the accretion disk is almost always formed for the fiduciary range of the physical parameters. We also find the conditions under which the disk formed from the tidal debris of a given star with a super Eddington accretion phase. We have simulated the light curve profiles in the relevant optical g band and soft X-rays for both super and sub-Eddington accretion disks as a function of M-dot (E,J,t). Using this, standard cosmological parameters, and mission instrument details, we predict the detectable TDE rates for various forthcoming surveys as a function of γ.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when its column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE MOSDEF SURVEY: DISSECTING THE STAR FORMATION RATE VERSUS STELLAR MASS RELATION USING Hα AND Hβ EMISSION LINES AT z ∼ 2

We present results on the star formation rate (SFR) versus stellar mass (M{sub *}) relation (i.e., the “main sequence”) among star-forming galaxies at 1.37 ≤ z ≤ 2.61 using the MOSFIRE Deep Evolution Field (MOSDEF) survey. Based on a sample of 261 galaxies with Hα and Hβ spectroscopy, we have estimated robust dust-corrected instantaneous SFRs over a large range in M{sub *} (∼10{sup 9.5}–10{sup 11.5} M{sub ⊙}). We find a correlation between log(SFR(Hα)) and log(M{sub *}) with a slope of 0.65 ± 0.08 (0.58 ± 0.10) at 1.4 < z < 2.6 (2.1 < z < 2.6). We find that different assumptions for the dust correction, such as using the color excess of the stellar continuum to correct the nebular lines, sample selection biases against red star-forming galaxies, and not accounting for Balmer absorption, can yield steeper slopes of the log(SFR)–log(M{sub *}) relation. Our sample is immune from these biases as it is rest-frame optically selected, Hα and Hβ are corrected for Balmer absorption, and the Hα luminosity is dust corrected using the nebular color excess computed from the Balmer decrement. The scatter of the log(SFR(Hα))–log(M{sub *}) relation, after accounting for the measurement uncertainties, is 0.31 dex at 2.1 < z < 2.6, which is 0.05 dex larger than the scatter in log(SFR(UV))–log(M{sub *}). Based on comparisons to a simulated SFR–M{sub *} relation with some intrinsic scatter, we argue that in the absence of direct measurements of galaxy-to-galaxy variations in the attenuation/extinction curves and the initial mass function, one cannot use the difference in the scatter of the SFR(Hα)– and SFR(UV)–M{sub *} relations to constrain the stochasticity of star formation in high-redshift galaxies.

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