Stellar Position Research Articles

Asymmetric Dust Accumulation of the PDS 70 Disk Revealed by ALMA Band 3 Observations

The PDS 70 system, hosting two planets within its disk, is an ideal target for examining the effect of planets on dust accumulation, growth, and ongoing planet formation. Here, we present high-resolution (0.″07 = 8 au) dust continuum observations of the PDS 70 disk in ALMA Band 3 (3.0 mm). While previous Band 7 observations showed a dust ring with slight asymmetry, our Band 3 observations reveal a more prominent asymmetric peak in the northwest direction, where the intensity is 2.5 times higher than in other directions and the spectral index is at the local minimum with α SED ∼ 2.2. This indicates that a substantial amount of dust is accumulated both radially and azimuthally in the peak. We also detect point-source emission around the stellar position in the Band 3 image, which is likely to be free–free emission. We constrain the eccentricity of the outer ring to be e < 0.04 from the position of the central star and the outer ring. From the comparison with numerical simulations, we constrain the mass of PDS 70c to be less than 4.9 MJupiter if the gas turbulence strength α turb = 10−3. Then, we discuss the formation mechanism of the disk structures and further planet formation scenarios in the disk.

Differential Rotation of CoRoT Stars and a Kepler Binary Star from Starspot Transit Mapping

Abstract While direct magnetic field measurements are rare for slowly rotating stars, spots observed during planetary transits provide a potential indicator of magnetic activity on stellar surfaces. Moreover, the rotation of the stellar surface can be probed by monitoring the spots’ position with time in subsequent transits. This study investigates the dynamic interplay of rotational shear and stellar rotation rate in six stars of spectral types F to M, all hosting exoplanets observed by the CoRoT space mission, except for one binary star from Kepler. The analysis, facilitated by the ECLIPSE code, unveils the physical properties of stellar spots, including radius, intensity, temperature, and position. The five CoRoT stars exhibit spot characteristics consistent with those observed in solar type stars. The determination of a spot longitude during different transits allows for the inference of the star’s differential rotation profile, revealing a decreasing trend of rotational shear with the mean stellar rotation period, given by Δ Ω ∝ P ¯ − 0.9 . This implies that, at least for slow rotators (mean rotation period &gt;5 days), as stars age, their differential rotation decreases. Additionally, the six stars analyzed here seem to fall into two categories, according to their spot flux deficit: those with ΔF spot &gt; 0.005 and those with ΔF spot &lt; 0.002.

First ALMA observations of the HD 105211 debris disc: A warm dust component close to a gigayear-old star

Most debris discs consist of a gas-poor, cold dust belt located tens to hundreds of astronomical units away from the host star. Many cold dust belts exhibit distinct structures attributed to the dynamic interaction of planetary systems. Moreover, in a few systems, additional warm components can be found closer to the central star, resembling the asteroid belt or zodiacal dust in our Solar System. In this work, we investigate the structure of the disc surrounding the nearby F2V star HD 105211 (eta Cru, HIP 59072), which has a warm excess (seen with Spitzer /MIPS at 24 mu m) and a potential asymmetry in the cold belt (seen in the Herschel /PACS images). We applied the CASA pipeline to obtain the ALMA 1.3 mm continuum images of HD105211. Then we constructed the spectral energy distribution (SED) of the system and performed Markov Chain Monte Carlo (MCMC) simulations to fit a model to the ALMA visibility data. To characterise the disc asymmetry, we analysed the ALMA images of two individual observation blocks (OB1, conducted on 2017 March 28, and OB2, conducted on 2018 May 9) and compared them to the previous Herschel images. Our modelling reveals that the disc around HD105211 is a narrow ring (23.6pm 4.6 au) with low eccentricity ($e positioned at a distance of 133.7pm 1.6 au from the central star, which differs from the broad disc ($100 au) starting at an inner edge of $87 au, inferred from the Herschel images. We found that both observation blocks show excess emission at the stellar position ($&gt;3 while OB1 shows an offset between the star and the phase centre ($ and OB2 shows brightness clumps ($ We used a two-temperature model to fit the infrared SED and used the ALMA detection to constrain the warm component to a nearly pure blackbody model. The relatively low ratio of actual radius to blackbody radius of the HD105211 debris disc indicates that this system is depleted in small grains, which could indicate that it is dynamically cold. The excess emission from the stellar position suggests that there should be a warm millimetre-sized dust component close to the star, for which we suggest two possible origins: in situ asteroid belt or comet delivery.

Galaxy main sequence and properties of low-mass Lyman-α emitters towards reionisation as viewed by VLT/MUSE and JWST/NIRCam

Context. Faint, star-forming galaxies are likely to play a dominant role in cosmic reionisation. Great strides have been made in recent years to characterise these populations at high redshifts (z &gt; 3). Now, for the first time, with JWST photometry beyond 1 μm in the rest frame, we can derive accurate stellar masses and position these galaxies on the galaxy main sequence. Aims. We seek to assess the place of 96 individual Lyman-α emitters (LAEs) selected behind the A2744 lensing cluster with MUSE IFU spectroscopy on the galaxy main sequence. We also compare the derived stellar masses to Lyman-α luminosities and equivalent widths to better quantify the relationship between the Lyman-α emission and the host galaxy. Methods. These 96 LAEs lie in the redshift range of 2.9 &lt; z &lt; 6.7, with their range of masses extending down to 106 M⊙ (over half with M⋆ &lt; 108 M⊙). We used the JWST/NIRCam and HST photometric catalogues from the UNCOVER project, giving us excellent wavelength coverage from 450 nm to 4.5 μm. We also performed an SED fitting using CIGALE, fixing the redshift of the LAEs to the secure, spectroscopic value. This combination of photometric coverage with spectroscopic redshifts allows us to robustly derive stellar masses for these galaxies. Results. We found a main sequence relation for these low-mass LAEs of log SFR = (0.88 ± 0.07 − 0.030 ± 0.027 × t) log M⋆ − (6.31 ± 0.41 − 0.08 ± 0.37 × t). This is in relative agreement with the best-fit results of prior collated studies; however, here we see a steeper slope and a higher normalisation. This indicates that low-mass LAEs towards the epoch of reionisation lie above the typical literature main sequence relations derived at lower redshift and higher masses. In addition, by comparing our results to UV-selected samples, we can see that while low-mass LAEs lie above these typical main sequence relations, they are likely not singular in this respect at these particular masses and redshifts. While low-mass galaxies have been shown to play a significant role in cosmic reionisation, our results point to the likelihood that LAEs hold no special position in this regard.

ALMA Reveals Hidden Morphologies in the Molecular Envelope of VY Canis Majoris

The J = 2 → 1 transition of CO near 230 GHz and the J = 3 → 2 line of HCN at 265 GHz have been imaged in the envelope of the red hypergiant star, VY Canis Majoris (VY CMa), using the Atacama Large Millimeter Array (ALMA) with angular resolutions 0.″2–1.″5; single-dish data were added to provide sensitivity up to 30″. These images reveal a far more complex envelope, with previously unseen outflows extending 4″–9″ from the star. These new structures include an arc-like outflow with an angular separation of ∼9″ northeast from the stellar position (“NE Arc”), twin fingerlike features approximately 4″ to the north/northeast (“NE Extension”), and a roughly spherical region observed ∼7″ E of the star (“E Bubble”). The NE Arc appears to be decelerating from base (V LSR ∼ 7 km s−1) to tip (V LSR ∼ 18 km s−1), while the NE Extension is blueshifted with V LSR ∼ −7 km s−1. Among the new features, HCN is only detected in the NE Arc. In addition, known structures Arc 1, Arc 2, and NW Arc, as well as other features closer to the star, are closely replicated in CO, suggesting that the gas and dust are well mixed. The CO spectra are consistent with the kinematic picture of VY CMa derived from HST data. Arc 2, however, has added complexity. Preliminary results from CO suggest 12C/13C ∼ 22–38 across the envelope. The additional presence of at least three major episodic mass ejection events significantly broadens the current perspective of the envelope structure and mass-loss history of VY CMa.

Compact Dust Emission in a Gravitationally Lensed Massive Quiescent Galaxy at z = 2.15 Revealed in ∼130 pc Resolution Observations by the Atacama Large Millimeter/submillimeter Array

We present new observations of MRG-M2129, a quiescent galaxy at z = 2.15, with the Atacama Large Millimeter/submillimeter Array (ALMA). With the combination of the effect of gravitational lensing by the foreground galaxy cluster and the angular resolution provided by ALMA, our data reveal 1.2 mm continuum emission at ∼130 pc angular resolution. Compact dust continuum is detected at 7.9σ in the target but displaced from its stellar peak position by 62 ± 38 mas, or ∼169 ± 105 pc in the source plane. We find a considerably high dust-to-stellar mass ratio, 4 × 10−4. From nondetection of the [C i] 3P2 → 3P1 line, we derive 3σ upper limits on the molecular gas-to-dust mass ratio δ GDR < 60 and the molecular gas-to-stellar mass ratio f H2 < 2.3%. The derived δ GDR is ≳2× smaller than the typical value assumed for quiescent galaxies in the literature. Our study supports the idea that there exists a broad range of δ GDR and urges submillimeter follow-up observations of quenching/recently quenched galaxies at similar redshifts. Based on the inferred low δ GDR and other observed properties, we argue that the central black hole is still active and regulates star formation in the system. Our study exhibits a rare case of a gravitationally lensed type 2 QSO harbored by a quiescent galaxy.

A Very Long Baseline Array Trigonometric Parallax for RR Aql and the Mira Period–Luminosity Relation

We report Very Long Baseline Array observations of 22 GHz H2O and 43 GHz SiO masers toward the Mira variable RR Aql. By fitting the SiO maser emission to a circular ring, we estimate the absolute stellar position of RR Aql and find agreement with Gaia astrometry to within the joint uncertainty of ≈1 mas. Using the maser astrometry we measure a stellar parallax of 2.44 ± 0.07 mas, corresponding to a distance of pc. The maser parallax deviates significantly from the Gaia EDR3 parallax of 1.95 ± 0.11 mas, indicating a 3.8σ tension between radio and optical measurements. This tension is most likely caused by optical photocenter variations limiting the Gaia astrometric accuracy for this Mira variable. Combining infrared magnitudes with parallaxes for RR Aql and other Miras, we fit a period–luminosity relation using a Bayesian approach with Markov Chain Monte Carlo sampling and a strong prior for the slope of −3.60 ± 0.30 from the Large Magellanic Cloud. We find a K-band zero-point (defined at logP(days) = 2.30) of −6.79 ± 0.15 mag using very long baseline interferometry (VLBI) parallaxes and −7.08 ± 0.29 mag using Gaia parallaxes. The Gaia zero-point is statistically consistent with the more accurate VLBI value.

Polarimetric detection of non-radial oscillation modes in the β Cephei star β Crucis

Here we report the detection of polarization variations due to nonradial modes in the beta Cephei star beta Crucis. In so doing we confirm 40-year-old predictions of pulsation-induced polarization variability and its utility in asteroseismology for mode identification. In an approach suited to other beta Cep stars, we combine polarimetry with space-based photometry and archival spectroscopy to identify the dominant nonradial mode in polarimetry, f2, as l = 3, m = -3 (in the m-convention of Dziembowski) and determine the stellar axis position angle as 25 (or 205) +/- 8 deg. The rotation axis inclination to the line of sight was derived as approx. 46 deg. from combined polarimetry and spectroscopy, facilitating identification of additional modes and allowing for asteroseismic modelling. This reveals a star of 14.5 +/- 0.5 Solar masses and a convective core containing approx. 28% of its mass -- making beta Crucis the most massive star with an asteroseismic age.

The porous envelope and circumstellar wind matter of the closest carbon star, CW Leonis

AbstractRecent abrupt changes of CW Leonis may indicate that we are witnessing the moment that the central carbon star is evolving off the Asymptotic Giant Branch (AGB) and entering into the pre-planetary nebula (PPN) phase. The recent appearance of a red compact peak at the predicted stellar position is possibly an unveiling event of the star, and the radial beams emerging from the stellar position resemble the feature of the PPN Egg Nebula. The increase of light curve over two decades is also extraordinary, and it is possibly related to the phase transition. Decadal-period variations are further found in the residuals of light curves, in the relative brightness of radial beams, and in the extended halo brightness distribution. Further monitoring of the recent dramatic and decadal-scale changes of this most well-known carbon star CW Leonis at the tip of AGB is still highly essential, and will help us gain a more concrete understanding on the conditions for transition between the late stellar evolutionary phases.

Multiepoch Optical Images of IRC+10216 Tell about the Central Star and the Adjacent Environment

Abstract Six images of IRC+10216 taken by the Hubble Space Telescope at three epochs in 2001, 2011, and 2016 are compared in the rest frame of the central carbon star. An accurate astrometry has been achieved with the help of Gaia Data Release 2. The positions of the carbon star in the individual epochs are determined using its known proper motion, defining the rest frame of the star. In 2016, a local brightness peak with compact and red nature is detected at the stellar position. A comparison of the color maps between 2016 and 2011 epochs reveals that the reddest spot moved along with the star, suggesting a possibility of it being the dusty material surrounding the carbon star. The relatively red, ambient region is distributed in an Ω shape and corresponds well to the dusty disk previously suggested based on near-infrared polarization observations. In a larger scale, differential proper motion of multiple ring-like patterns in the rest frame of the star is used to derive the average expansion velocity of transverse wind components, resulting in ∼12.5 km s−1(d/123 pc), where d is the distance to IRC+10216. Three-dimensional geometry is implied from its comparison with the line-of-sight wind velocity determined from half widths of submillimeter emission line profiles of abundant molecules. Uneven temporal variations in brightness for different searchlight beams and anisotropic distribution of the extended halo are revisited in the context of the stellar light illumination through a porous envelope with postulated longer-term variations for a period of ≲10 yr.

Evidence for an MHD Disk Wind via Optical Forbidden Line Spectroastrometry*

Abstract Spectroastrometry is used to investigate the low-velocity component (LVC) of the optical forbidden emission from the T Tauri stars RU Lupi and AS 205 N. Both stars also have high-velocity forbidden emission, which is tracing a jet. For AS 205 N, analysis reveals a complicated outflow system. For RU Lupi, the [O i] λ6300 and [S ii]λλ6716,6731 LV narrow component (NC) is offset along the same position angle (PA) as the high-velocity component but with a different velocity gradient than the jet, in that displacement from the stellar position along the rotation axis is decreasing with increasing velocity. From the LVC, NC, PA, and velocity gradient, it is inferred that the NC is tracing a wide-angled magnetohydrodynamic (MHD) disk wind. A photoevaporative wind is ruled out. This is supported by a comparison with a previous spectroastrometric study of the CO fundamental line. The decrease in offset with increasing velocity is interpreted as tracing an increase in the height of the wind with increasing disk radius. This is one of the first measurements of the spatial extent of the forbidden emission line LVC NC (∼40 au, 8 au for RU Lupi in the [S ii] λ6731 and [O i] λ6300 lines) and the first direct confirmation that the LVC narrow component can trace an MHD disk wind.

When the Peas Jump around the Pod: How Stellar Clustering Affects the Observed Correlations between Planet Properties in Multiplanet Systems

Abstract Recent studies have shown that the radii and masses of adjacent planets within a planetary system are correlated. It is unknown how this “peas-in-a-pod” phenomenon originates, whether it is in place at birth or requires evolution, and whether it (initially) applies only to neighboring planets or to all planets within a system. Here we address these questions by making use of the recent discovery that planetary system architectures strongly depend on ambient stellar clustering. Based on Gaia's second data release, we divide the sample of planetary systems hosting multiple planets into those residing in stellar position–velocity phase space overdensities and the field, representing samples with elevated and low degrees of external perturbation, respectively. We demonstrate that the peas-in-a-pod phenomenon manifests itself in both samples, suggesting that the uniformity of planetary properties within a system is not restricted to direct neighbors and likely already exists at birth. The radius uniformity is significantly elevated in overdensities, suggesting that it can be enhanced by evolutionary effects that either have a similar impact on the entire planetary system or favor the retention of similar planets. The mass uniformity may exhibit a similar, but weaker dependence. Finally, we find ordering in both samples, with the planet radius and mass increasing outwards. Despite its prevalence, the ordering is somewhat weaker in overdensities, suggesting that it may be disrupted by external perturbations arising from stellar clustering. We conclude that a comprehensive understanding of the peas-in-a-pod phenomenon requires linking planet formation and evolution to the large-scale stellar and galactic environment.

Apuntes críticos sobre el control judicial de constitucionalidad en el Ecuador

La aprobación de la Constitución de la República del Ecuador (CRE) en el año 2008 marcó un giro transcendental en el paradigma del derecho constitucional ecuatoriano. A partir de este momento, y a la luz del nuevo estado de derechos y justicia social consagrado en la Constitución, se concibe por primera vez a la Corte Constitucional (CC) como un organismo especializado e independiente de las demás funciones del Estado. Es preciso dejar sentado que durante el siglo XX también se instituyeron Tribunales Constitucionales, sin embargo, la estructura y atribuciones de estos no eran precisamente los de un organismo de jurisdicción constitucional que ejerce su acción de forma plena. Así, en la Constitución de 1945 se crea el Tribunal de Garantías Constitucionales (TGC) como un órgano de control constitucional, dependiente de los demás poderes del Estado, con escasas competencias para realizar el control sobre la ley. En el presente artículo se realizará un breve análisis de la evolución de la jurisdicción constitucional en el Ecuador. A partir de la Constitución de 2008, la forma de concebir la organización del Estado en el Ecuador tiene un impacto directo sobre el control judicial de constitucionalidad, dado que todos los jueces ocupan un sitio estelar como custodios de los derechos de quienes acuden ante la administración judicial. Así sucede, al menos, en el plano formal, pues en la práctica jurisdiccional existe una brecha marcada entre el diseño formal y la materialización del estado de derechos. No obstante, la declaración de inconstitucionalidad de la ley es una competencia exclusiva de la Corte Constitucional. Los jueces de los distintos tribunales se limitan a realizar un trabajo colaborativo con el órgano encargado de la jurisdicción constitucional. Dicho esto, se ha proscrito de manera tajante la posibilidad de que los jueces ordinarios declaren la inconstitucionalidad de cualquier norma jurídica.&#x0D; Recibido: 20.11.2020Aceptado: 21.12.2020

The impact of merging on the origin of kinematically misaligned and counter-rotating galaxies in MaNGA

ABSTRACT Galaxy mergers and interactions are expected to play a significant role leading to offsets between gas and stellar motions in galaxies. Herein, we cross-match galaxies in Mapping Nearby Galaxies at Apache Point Observatory MPL-8 with the Dark Energy Spectroscopic Instrument Legacy Surveys and identify 311 merging galaxies that have reliable measurements of ΔPA, the difference between the stellar and gas kinematic position angles, to investigate the impacts of merging on gas–stellar rotation misalignments. We find that the merging fractions of misaligned galaxies (30$^\circ \, \leqslant \, \Delta$PA &amp;lt; 150○) are higher than those of co-rotators (ΔPA &amp;lt; 30○) in both quiescent and star-forming galaxies. This result suggests that merging is one process to produce kinematic misalignments. The merging fraction of counter-rotators (ΔPA ≥ 150○) is lower than that of misaligned galaxies in both quiescent and star-forming galaxies, while in the latter it is likely even lower than that of co-rotators. The orbital angular momentum transfer to the spins of stars and gas during merging and the tidal feature disappearance can lead to small merging fractions in counter-rotators. Numerous new stars that inherit angular momentum from gas after merging can further lower the merging fraction of star-forming counter-rotators.

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Constraining the Molecular Content at log(M*/M⊙) ∼ 9.5 with CO Stacking of MUSE-detected z ∼ 1.5 Galaxies

Abstract We report molecular gas mass estimates obtained from a stacking analysis of CO line emission in the ALMA Spectroscopic Survey (ASPECS) using the spectroscopic redshifts from the optical integral field spectroscopic survey by the Multi Unit Spectroscopic Explorer (MUSE) of the Hubble Ultra Deep Field (HUDF). Stacking was performed on subsets of the sample of galaxies classified by their stellar mass and position relative to the main-sequence relation (on, above, below). Among all the CO emission lines, from CO(2–1) to CO(6–5), with redshifts accessible via the ASPECS Band 3 and the MUSE data, CO(2–1) provides the strongest constraints on the molecular gas content. We detect CO(2–1) emission in galaxies down to stellar masses of . Below this stellar mass, we present a new constraint on the molecular gas content of main-sequence galaxies by stacking based on the MUSE detections. We find that the molecular gas mass of main-sequence galaxies continuously decreases with stellar mass down to . Assuming a metallicity-based CO–to–H 2 conversion factor, the molecular gas-to-stellar mass ratio from to ∼10.0 does not seem to decrease as fast as for , which is in line with simulations and studies at lower redshift. The inferred molecular gas density of MUSE-selected galaxies at is comparable with the one derived in the HUDF with a different CO selection. Using the MUSE data we recover most of the CO emission in our deep ALMA observations through stacking, demonstrating the synergy between volumetric surveys obtained at different wave bands.

Spectral Energy Distribution of Blue Stragglers in the Core of 47 Tucanae

Abstract We have constructed the spectral energy distributions (SEDs) of a sample of blue straggler stars (BSSs) in the core of the globular cluster 47 Tucanae, taking advantage of the large set of high resolution images, ranging from the ultraviolet to the near-infrared, obtained with the Advanced Camera for Surveys/High Resolution Channel of the Hubble Space Telescope. Our final BSS sample consists of 22 objects, spanning the whole color and magnitude extension of the BSS sequence in 47 Tucanae. We fitted the BSS broadband SEDs with models to derive temperature, surface gravity, radius, luminosity, and mass. We show that BSSs indeed define a mass sequence, where the mass increases for increasing luminosity. Interestingly, the BSS mass estimates from the SED fitting turn out to be comparable to those derived from the projection of the stellar position in the color–magnitude diagram on standard star evolutionary tracks. We compare our results with previous, direct mass estimates of a few BSSs in 47 Tucanae. We also find a couple of supermassive BSS candidates, i.e., BSSs with masses larger than twice the turn-off mass, the formation of which must have involved more than two progenitors.

Comparison of astronomical software programs for archaeoastronomical applications

Abstract Reproducing the movements of stars and planets across the sky has recently had notable insights thanks to the widespread use of astronomical software products with high mapping and graphical capabilities. Nonetheless, when it is necessary to determine the position of a star in the very remote past (or future), one must take into account two factors which have a profound impact on stellar positioning: the precession of the equinoxes and the proper motions of the stars, two mechanisms that are not always been properly considered, especially in the archaeoastronomical literature. The present work compares the principal commercial astronomical programs currently available with the goal to determine how correctly they evaluate the two aforementioned mechanisms. The comparison is carried out on a sample of 24 stars (among the brightest in the sky) using a subroutine which carefully evaluates the two phenomena. A discussion on the principal methods used to approximate precession is also given. The differences observed between the values of declination calculated with various approximations, as well as those between different astronomical software programs, may even exceed one degree, a value that is far beyond the resolving power of the human eye, making the evaluations and the consequent conclusions unreliable. Furthermore, via a reconstruction of the temporal trends of declination in the interval [25000 BC; AD 25000] for two stars with the highest (Toliman, α Cen) and the lowest (Mintaka, δ Ori) proper motions, the consequences of this effect on the stellar position are evaluated. Finally, as a consequence of the presented evidence, we test some alignments towards the brightest stars of the sky proposed for some enclosures of Gobekli Tepe, the most ancient megalithic site in the world.

Unlocking the secrets of the midplane gas and dust distribution in the young hybrid disc HD 141569

Context. HD 141569 is a pre-main sequence star with a disc uniquely placed between protoplanetary and debris discs, similar to the older “hybrid” type discs. Aims. This work aims to place the mass and spatial structure of the disc midplane in the context of the debris, hybrid and protoplanetary discs. Methods. We observed HD 141569 with ALMA in 1.3 mm continuum and 13CO (2-1). This is the first detection and image of the optically thin gas emission from the midplane of this disc. Results. In continuum emission, we detect a combination of an unresolved central peak and a ring of millimetre emission at 220 ± 10 au, slightly interior to one of the rings discovered in scattered light. The minimum dust mass of the ring is 0.13 ± 0.02 M⊕ while the unresolved millimetre peak at the stellar location is predominantly thermal emission due to a minimum of 1.2 ± 0.2 M⊕ of dust. 13CO is distributed asymmetrically around the stellar position with a peak at 1ʺ̣1 distance and a PA of −33°. The gas is detected as far as 220 ± 10 au, a radial separation the same as that of the mm ring. Assuming optically thin emission and standard ISM abundances, we used our 13CO data to derive the gas mass in the disc of (6.0 ± 0.9) × 10−4M⊙. Comparison to published 12CO data shows that 12CO is optically thick, explaining why estimates based on 12CO underestimated the gas mass.

A radial velocity survey of the Carina Nebula's O-type stars

We have obtained multi-epoch observations of 31 O-type stars in the Carina Nebula using the CHIRON spectrograph on the CTIO/SMARTS 1.5-m telescope. We measure their radial velocities to 1--2 km s$^{-1}$ precision and present new or updated orbital solutions for the binary systems HD 92607, HD 93576, HDE 303312, and HDE 305536. We also compile radial velocities from the literature for 32 additional O-type and evolved massive stars in the region. The combined data set shows a mean heliocentric radial velocity of 0.6 km s$^{-1}$. We calculate a velocity dispersion of $\le9.1$ km s$^{-1}$, consistent with an unbound, substructured OB association. The Tr 14 cluster shows a marginally significant 5 km s$^{-1}$ radial velocity offset from its neighbor Tr 16, but there are otherwise no correlations between stellar position and velocity. The O-type stars in Cr 228 and the South Pillars region have a lower velocity dispersion than the region as a whole, supporting a model of distributed massive-star formation rather than migration from the central clusters. We compare our stellar velocities to the Carina Nebula's molecular gas and find that Tr 14 shows a close kinematic association with the Northern Cloud. In contrast, Tr 16 has accelerated the Southern Cloud by 10--15 km s$^{-1}$, possibly triggering further massive-star formation. The expansion of the surrounding H II region is not symmetric about the O-type stars in radial velocity space, indicating that the ionized gas is constrained by denser material on the far side.

The Intrinsic Characteristics of Galaxies on the SFR–M∗ Plane at 1.2 &lt; z &lt; 4: I. The Correlation between Stellar Age, Central Density, and Position Relative to the Main Sequence

Abstract We use the deep CANDELS observations in the GOODS North and South fields to revisit the correlations between stellar mass (M *), star formation rate (SFR) and morphology, and to introduce a fourth dimension, the mass-weighted stellar age, in galaxies at . We do this by making new measures of M *, SFR, and stellar age thanks to an improved SED fitting procedure that allows various star formation history for each galaxy. Like others, we find that the slope of the main sequence (MS) of star formation in the plane bends at high mass. We observe clear morphological differences among galaxies across the MS, which also correlate with stellar age. At all redshifts, galaxies that are quenching or quenched, and thus old, have high (the projected density within the central 1 kpc), while younger, star-forming galaxies span a much broader range of , which includes the high values observed for quenched galaxies, but also extends to much lower values. As galaxies age and quench, the stellar age and the dispersion of for fixed values of M * shows two different regimes: one at the low-mass end, where quenching might be driven by causes external to the galaxies; the other at the high-mass end, where quenching is driven by internal causes, very likely the mass given the low scatter of (mass quenching). We suggest that the monotonic increase of central density as galaxies grow is one manifestation of a more general phenomenon of structural transformation that galaxies undergo as they evolve.