- ID:
- ivo://CDS.VizieR/J/ApJ/748/14
- Title:
- ONC population data from WFI observations
- Short Name:
- J/ApJ/748/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new census of the Orion Nebula Cluster over a large field of view (>~30'x30'), significantly increasing the known population of stellar and substellar cluster members with precisely determined properties. We develop and exploit a technique to determine stellar effective temperatures from optical colors, nearly doubling the previously available number of objects with effective temperature determinations in this benchmark cluster. Our technique utilizes colors from deep photometry in the I band and in two medium-band filters at {lambda}~753 and 770nm, which accurately measure the depth of a molecular feature present in the spectra of cool stars. From these colors we can derive effective temperatures with a precision corresponding to better than one-half spectral subtype, and importantly this precision is independent of the extinction to the individual stars. Also, because this technique utilizes only photometry redward of 750nm, the results are only mildly sensitive to optical veiling produced by accretion. Completing our census with previously available data, we place some 1750 sources in the Hertzsprung-Russell diagram and assign masses and ages down to 0.02M_{sun}_. At faint luminosities, we detect a large population of background sources which is easily separated in our photometry from the bona fide cluster members. The resulting initial mass function of the cluster has good completeness well into the substellar mass range, and we find that it declines steeply with decreasing mass. This suggests a deficiency of newly formed brown dwarfs in the cluster compared to the Galactic disk population.
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- ID:
- ivo://CDS.VizieR/J/ApJ/722/1092
- Title:
- Optical photometry of the ONC. II.
- Short Name:
- J/ApJ/722/1092
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new analysis of the stellar population of the Orion Nebula Cluster (ONC) based on multi-band optical photometry and spectroscopy. We study the color-color diagrams in BVI, plus a narrowband filter centered at 6200{AA}, finding evidence that intrinsic color scales valid for main-sequence dwarfs are incompatible with the ONC in the M spectral-type range, while a better agreement is found employing intrinsic colors derived from synthetic photometry, constraining the surface gravity value as predicted by a pre-main-sequence isochrone. We refine these model colors even further, empirically, by comparison with a selected sample of ONC stars with no accretion and no extinction. We consider the stars with known spectral types from the literature, and extend this sample with the addition of 65 newly classified stars from slit spectroscopy and 182 M-type from narrowband photometry; in this way, we isolate a sample of about 1000 stars with known spectral type. We introduce a new method to self-consistently derive the stellar reddening and the optical excess due to accretion from the location of each star in the BVI color-color diagram. This enables us to accurately determine the extinction of the ONC members, together with an estimate of their accretion luminosities. We adopt a lower distance for the Orion Nebula than previously assumed, based on recent parallax measurements. With a careful choice of also the spectral-type-temperature transformation, we produce the new Hertzsprung-Russell diagram of the ONC population, more populated than previous works.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/46
- Title:
- Opt. photometry of SMUDGes ultra-diffuse galaxies
- Short Name:
- J/ApJS/247/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first systematic study of the stellar populations of ultra-diffuse galaxies (UDGs) in the field, integrating the large area search and characterization of UDGs by the SMUDGes survey with the twelve-band optical photometry of the S-PLUS survey. Based on Bayesian modeling of the optical colors of UDGs, we determine the ages, metallicities, and stellar masses of 100 UDGs distributed in an area of ~330deg^2^ in the Stripe 82 region. We find that the stellar masses and metallicities of field UDGs are similar to those observed in clusters and follow the trends previously defined in studies of dwarf and giant galaxies. However, field UDGs have younger luminosity- weighted ages than do UDGs in clusters. We interpret this result to mean that field UDGs have more extended star formation histories, including some that continue to form stars at low levels to the present time. Finally, we examine stellar population scaling relations that show that UDGs are, as a population, similar to other low surface brightness galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A45
- Title:
- Orion optical-depth and column-density maps
- Short Name:
- J/A+A/566/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution, high dynamic range column-density and color-temperature maps of the Orion complex using a combination of Planck dust-emission maps, Herschel dust-emission maps, and 2MASS NIR dust-extinction maps. The column-density maps combine the robustness of the 2MASS NIR extinction maps with the resolution and coverage of the Herschel and Planck dust-emission maps and constitute the highest dynamic range column-density maps ever constructed for the entire Orion complex, covering 0.01mag<A_K_<30mag, or 2x10^20^cm^-2^<N<5x10^23^cm^-2^. We determined the ratio of the 2.2{mu}m extinction coefficient to the 850{mu}m opacity and found that the values obtained for both Orion A and B are significantly lower than the predictions of standard dust models, but agree with newer models that incorporate icy silicate-graphite conglomerates for the grain population. We show that the cloud projected probability distribution function, over a large range of column densities, can be well fitted by a simple power law. Moreover, we considered the local Schmidt-law for star formation, and confirm earlier results, showing that the protostar surface density {Sigma}_*_ follows a simple law {Sigma}_*_{prop.to}{Sigma}_gas_^{beta}^, with {beta}~2.
- ID:
- ivo://CDS.VizieR/J/ApJ/892/23
- Title:
- Pa-beta, Ha and attenuation in NGC5194 & NGC6946
- Short Name:
- J/ApJ/892/23
- Date:
- 19 Jan 2022 08:58:18
- Publisher:
- CDS
- Description:
- We combine Hubble Space Telescope Paschen {beta} (Pa{beta}) imaging with ground-based, previously published H{alpha} maps to estimate the attenuation affecting H{alpha}, A(H{alpha}), across the nearby, face-on galaxies NGC 5194 and NGC 6946. We estimate A(H{alpha}) in ~2000 independent 2" ~75pc diameter apertures in each galaxy, spanning out to a galactocentric radius of almost 10kpc. In both galaxies, A(H{alpha}) drops with radius, with a bright, high-attenuation inner region, though in detail the profiles differ between the two galaxies. Regions with the highest attenuation-corrected H{alpha} luminosity show the highest attenuation, but the observed H{alpha} luminosity of a region is not a good predictor of attenuation in our data. Consistent with much previous work, the IR-to-H{alpha} color does a good job of predicting A(H{alpha}). We calculate the best-fit empirical coefficients for use combining H{alpha} with 8, 12, 24, 70, or 100{mu}m to correct for attenuation. These agree well with previous work, but we also measure significant scatter around each of these linear relations. The local atomic plus molecular gas column density, N(H), also predicts A(H{alpha}) well. We show that a screen with magnitude ~0.2 times that expected for a Milky Way gas-to-dust value does a reasonable job of explaining A(H{alpha}) as a function of N(H). This could be expected if only ~40% of gas and dust directly overlap regions of H{alpha} emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/884/136
- Title:
- PAH features of star-forming gal. using Spitzer/IRS
- Short Name:
- J/ApJ/884/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Polycyclic aromatic hydrocarbon (PAH) emission has long been proposed to be a potential star formation rate indicator, as it arises from the photodissociation region bordering the Stromgren sphere of young, massive stars. We apply a recently developed technique of mid-infrared spectral decomposition to obtain a uniform set of PAH measurements from Spitzer low-resolution spectra of a large sample of star-forming galaxies spanning a wide range in stellar mass (M_*_~10^6^-10^11.4^M_{sun}_) and star formation rate (~0.1-2000M_{sun}_/yr). High-resolution spectra are also analyzed to measure [NeII]12.8{mu}m and [NeIII]15.6{mu}m, which effectively trace the Lyman continuum. We present a new relation between PAH luminosity and star formation rate based on the [NeII] and [NeIII] lines. Calibrations are given for the integrated 5-15{mu}m PAH emission, the individual features at 6.2, 7.7, 8.6, and 11.3{mu}m, as well as several mid- infrared bandpasses sensitive to PAH. We confirm that PAH emission is suppressed in low-mass dwarf galaxies, and we discuss the possible physical origin of this effect.
- ID:
- ivo://CDS.VizieR/J/ApJ/788/154
- Title:
- Palomar Transient Factory SNe IIn photometry
- Short Name:
- J/ApJ/788/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interaction of supernova (SN) ejecta with the optically thick circumstellar medium (CSM) of a progenitor star can result in a bright, long-lived shock-breakout event. Candidates for such SNe include Type IIn and superluminous SNe. If some of these SNe are powered by interaction, then there should be a specific relation between their peak luminosity, bolometric light-curve rise time, and shock-breakout velocity. Given that the shock velocity during shock breakout is not measured, we expect a correlation, with a significant spread, between the rise time and the peak luminosity of these SNe. Here, we present a sample of 15 SNe IIn for which we have good constraints on their rise time and peak luminosity from observations obtained using the Palomar Transient Factory. We report on a possible correlation between the R-band rise time and peak luminosity of these SNe, with a false-alarm probability of 3%. Assuming that these SNe are powered by interaction, combining these observables and theory allows us to deduce lower limits on the shock-breakout velocity. The lower limits on the shock velocity we find are consistent with what is expected for SNe (i.e., ~10^4^ km/s). This supports the suggestion that the early-time light curves of SNe IIn are caused by shock breakout in a dense CSM. We note that such a correlation can arise from other physical mechanisms. Performing such a test on other classes of SNe (e.g., superluminous SNe) can be used to rule out the interaction model for a class of events.
- ID:
- ivo://CDS.VizieR/J/AJ/152/19
- Title:
- Pan-Pacific Planet Search (PPPS). V. 164 stars
- Short Name:
- J/AJ/152/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectroscopic stellar parameters for the complete target list of 164 evolved stars from the Pan-Pacific Planet Search, a five-year radial velocity campaign using the 3.9m Anglo-Australian Telescope. For 87 of these bright giants, our work represents the first determination of their fundamental parameters. Our results carry typical uncertainties of 100K, 0.15dex, and 0.1dex in T_eff_, logg, and [Fe/H] and are consistent with literature values where available. The derived stellar masses have a mean of 1.31_-0.25_^+0.28^M_{Sun}_, with a tail extending to ~2M_{Sun}_, consistent with the interpretation of these targets as "retired" A-F type stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/97
- Title:
- Photospheric properties of T Tauri stars
- Short Name:
- J/ApJ/786/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Estimates of the mass and age of young stars from their location in the H-R diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux-calibrated optical spectra to measure accurate spectral types and extinctions of 281 nearby T Tauri stars (TTSs). The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars, many of which are well known and can serve as benchmarks. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are one to two subclasses later than literature spectral types for the original members of the TW Hya Association (TWA) and are discrepant with literature values for some well-known members of the Taurus Molecular Cloud. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than near-IR measurements, likely the result of methodological differences and the presence of near-IR excesses in most CTTSs. As an illustration of the impact of accretion, spectral type, and extinction uncertainties on the H-R diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15%-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to significantly alter the subsequent evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A24
- Title:
- Pipe nebula optical-depth, column-density maps
- Short Name:
- J/A+A/620/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multi-wavelength observations in the sub-mm regime provide information on the distribution of both the dust column density and the effective dust temperature in molecular clouds. In this study, we created high-resolution and high-dynamic-range maps of the Pipe nebula region and explored the value of dust-temperature measurements in particular towards the dense cores embedded in the cloud. The maps are based on data from the Herschel and Planck satellites, and calibrated with a near-infrared extinction map based on 2MASS observations. We have considered a sample of previously defined cores and found that the majority of core regions contain at least one local temperature minimum. Moreover, we observed an anti-correlation between column density and temperature. The slope of this anti-correlation is dependent on the region boundaries and can be used as a metric to distinguish dense from diffuse areas in the cloud if systematic effects are addressed appropriately. Employing dust-temperature data thus allows us to draw conclusions on the thermodynamically dominant processes in this sample of cores: external heating by the interstellar radiation field and shielding by the surrounding medium. In addition, we have taken a first step towards a physically motivated core definition by recognising that the column-density-temperature anti-correlation is sensitive to the core boundaries. Dust-temperature maps therefore clearly contain valuable information about the physical state of the observed medium.
