We present a first-order analytical model for line-of-sight velocity residuals, defined as the difference between observed velocities and those predicted by a fiducial model, assuming a flared, nearly axisymmetric disk with the perturbations in disk surface height $δh(r)$, inclination $δi(r)$, and position angle $δ\mathrm{PA}(r)$. Introducing projection-deprojection mapping between sky-plane and disk-frame coordinates, we demonstrate that the normalized velocity residuals exhibit Fourier components up to the third harmonic ($\sin3φ$ and $\cos3φ$). Moreover, we show that the radial profiles of $δh(r)$, $δi(r)$, and $δ\mathrm{PA}(r)$ can be uniquely recovered from the data by solving a linear inverse problem. For comparison, we highlight factors that are not considered in previous models. We also outline how our framework can be extended beyond the first-order residuals and applied to additional observables, such as line intensities and widths.
O Sol e as estrelas apresentam atividade magnética na forma de manchas escuras em sua superfície, além de produzirem explosões e ejeções de massa de suas atmosferas. As assinaturas de manchas escuras na superfície das estrelas podem ser modeladas a fim de caraterizar seus tamanhos e temperaturas. Estrelas jovens e anãs M produzem energéticas superexplosões, as quais podem impactar os planetas em órbitas, principalmente os que estiverem bem próximos da sua estrela hospedeira. O fluxo de radiação ultravioleta destas explosões pode ser prejudicial para possíveis organismos vivos na superfície de exoplanetas orbitando na zona habitável de estrelas ativas. Entretanto, uma atmosfera com ozônio poderia protegê-los, ou então um oceano. Os ventos estelares também afetam as atmosferas planetárias, podendo ser responsáveis pela sua erosão.
Gemma González-Torà, Ben Davies, Rolf-Peter Kudritzki
et al.
The temperatures of red supergiants (RSGs) are expected to depend on metallicity (Z) in such a way that lower-Z RSGs are warmer. In this work, we investigate the Z-dependence of the Hayashi limit by analysing RSGs in the low-Z galaxy Wolf-Lundmark-Mellote (WLM), and compare with the RSGs in the higher-Z environments of the Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC). We determine the effective temperature ($T_{\textrm{eff}}$) of each star by fitting their spectral energy distributions, as observed by VLT+SHOOTER, with MARCS model atmospheres. We find average temperatures of $T_{\textrm{eff}_{\textrm{WLM}}}=4400\pm202$ K, $T_{\textrm{eff}_{\textrm{SMC}}}=4130\pm103$ K, and $T_{\textrm{eff}_{\textrm{LMC}}}=4140\pm148$ K. From population synthesis analysis, we find that although the Geneva evolutionary models reproduce this trend qualitatively, the RSGs in these models are systematically too cool. We speculate that our results can be explained by the inapplicability of the standard solar mixing length to RSGs.
Neste artigo são revistos os principais eventos que teriam ocorrido nas primeiras fases de evolução do universo, quando o plasma cósmico é opaco à radiação eletromagnética. Neste caso, a informação sobre tais eventos não pode provir de fótons mas somente de ondas gravitacionais, detetadas pela primeira vez em 2015. Serão revisitados os espectros do fundo de ondas gravitacionais gerados durante o período inflacionário e as transições de fase eletrofraca e quark-hádron. Além disso, são examinados os espectros do fundo de ondas gravitacionais gerados em cenários alternativos ao \textit{big bang}, sugeridos por teorias efetivas de campo.
We present SOFIA/FIFI-LS observations of five prototypical, low-mass Class I outflows (HH111, SVS13, HH26, HH34, HH30) in the far-infrared [OI]63mum and [OI]145mum transitions. The obtained spectroscopic [OI]63mum and [OI]145mum maps enable us to study the spatial extent of warm, low-excitation atomic gas within outflows driven by Class I protostars. These [OI] maps may potentially allow us to measure the mass-loss rates ($\dot{M}_\text{jet}$) of this warm component of the atomic jet.
We observe the S-cluster star S62 on its Keplerian orbit around the supermassive black hole in the center of our galaxy, SgrA*. The orbital time period of S62 around SgrA* is 9.9 years. We derive its mass to be around 2 M_solar which is consistent with other members of the S-cluster. From the Lucy-Richardson deconvolved images, we determine a K-band magnitude of 16.1 mag. We observe almost two complete orbits of the star with two different and independent telescopes and three different instruments. The close distance of S62 to SgrA* at its periapse of around 2 mas results in a gravitational periapse shift of almost 10%/orbit.
Accretion disks are one of the key ingredients of the star formation process. They redistribute angular momentum and, in the case of high-mass stars (M > 8Msun), disks would relieve the radiation pressure on the accreting material, in particular in the equatorial direction, by beaming the radiation through the poles of the system and this would allow the accretion to proceed onto the central protostar (e.g., Tan et al. 2014 for a review on massive star formation). In fact, in recent years, all high-mass star-forming theories appear to converge to a disk-mediated accretion scenario (e.g., Krumholz et al. 2007; Kuiper et al. 2011; Bonnell & Bate 2006; Keto 2007) but do the observations of high-mass young stellar objects (YSOs) confirm the theory predictions? Or in other words, do true accretion disks around massive stars really exist?
White dwarfs are the remnants of low and intermediate mass stars. Because of electron degeneracy, their evolution is just a simple gravothermal process of cooling. Recently, thanks to Gaia data, it has been possible to construct the luminosity function of massive (0.9 < M/Msun < 1.1) white dwarfs in the solar neighborhood (d < 100 pc). Since the lifetime of their progenitors is very short, the birth times of both, parents and daughters, are very close and allow to reconstruct the (effective) star formation rate. This rate started growing from zero during the early Galaxy and reached a maximum 6-7 Gyr ago. It declined and ~5 Gyr ago started to climb once more reaching a maximum 2 - 3 Gyr in the past and decreased since then. There are some traces of a recent star formation burst, but the method used here is not appropriate for recently born white dwarfs.
P. J. A. Lago, R. D. D. Costa, M. Faúndez-Abans
et al.
High nitrogen abundance is characteristic of Type I planetary nebulae as well as their highly filamentary structure. In the present work we test the hypothesis of shocks as a relevant excitation mechanism for a Type-I nebula, NGC 6302, using recently released diagnostic diagrams to distinguish shocks from photoexcitation. The construction of diagrams depends on emission line ratios and kinematical information. NGC 6302 shows the relevance of shocks in peripheral regions and the importance to the whole nebula. Using shocks, we question the usual assumption of ICF calculation, justifying a warning to broadly used abundance derivation methods. From a kinematical analysis, we derive a new distance for NGC 6302 of $805\pm143\,$ pc.
We report on the detection of a stellar halo around NGC 1560, a 10^9 Mo spiral galaxy member of the Maffei group. We obtained deep images in the r and i bands using the 10.4m Gran Telescopio Canarias in a field centered at ~ 3.7 arcmin (projected distance of 3.5 kpc) from the center of this galaxy. The luminosity function and the CMD show a clear excess of stars with respect to the expected foreground level at magnitudes fainter than the RGB tip at the distance of NGC 1560. The color of the halo stars implies a metallicity of Z ~ Zo/50, while their counts correspond to a stellar mass of ~ 10^7 Mo in the sampled region. Assuming a power law profile for the surface mass density of the halo, our data suggest a total stellar mass of 10^8 Mo for the halo of NGC 1560.
Observations of star-forming galaxies in the distant Universe (z > 2) are starting to confirm the importance of massive stars in shaping galaxy emission and evolution. Inevitably, these distant stellar populations are unresolved, and the limited data available must be interpreted in the context of stellar population synthesis models. With the imminent launch of JWST and the prospect of spectral observations of galaxies within a gigayear of the Big Bang, the uncertainties in modelling of massive stars are becoming increasingly important to our interpretation of the high redshift Universe. In turn, these observations of distant stellar populations will provide ever stronger tests against which to gauge the success of, and flaws in, current massive star models.
Two approaches are suggested for recording the continuum corona in the range < 1.4 Rsun. They are different from the classical coronagraphic ones. Current state in the thin film technology allows discussing a new generation coronagraph with a variable transmission of an entrance aperture. The estimated coronagraphic factor is 2 orders of magnitude higher compared to a Lyot-type coronagraph. Another approach is based on the use of total solar eclipses at near-Mercury orbits. The instrumental background is decreased at least 3 orders of magnitude. That allows using a more simplified optical sketch.
The use of Reduced Proper Motion in identifying isolated white dwarfs has long been used as a proxy for the absolute magnitude in a population with known kinematics. This, however, introduces a proper motion detection limit on top of the existing photometric limit. How the survey volume is hampered by this extra parameter is discussed in Hambly et al. 2012. In this work, we discuss some robust outlier rejection methods in order to minimise the proper motion limit and hence maximise the survey volume. The generalised volume, corrected for the distance of the Sun from the Galactic Plane, is integrated explicitly.
Diagnostic radiology and radiation oncology are arguably two of the most technologically advanced specialties in medicine. The imaging and radiation medicine technologies in clinical use today have been continuously improved through new advances made in the commercial and academic research arenas. This symposium explores the translational path from research through clinical implementation. Dr. Pettigrew will start this discussion by sharing his perspectives as director of the National Institute of Biomedical Imaging and Bioengineering (NIBIB). The NIBIB has focused on promoting research that is technological in nature and has high clinical impact. We are in the age of precision medicine, and the technological innovations and quantitative tools developed by engineers and physicists working with physicians are providing innovative tools that increase precision and improve outcomes in health care. NIBIB funded grants lead to a very high patenting rate (per grant dollar), and these patents have higher citation rates by other patents, suggesting greater clinical impact, as well.Two examples of clinical translation resulting from NIH‐funded research will be presented, in radiation therapy and diagnostic imaging. Dr. Yu will describe a stereotactic radiotherapy device developed in his laboratory that is designed for treating breast cancer with the patient in the prone position. It uses 36 rotating Cobalt‐60 sources positioned in an annular geometry to focus the radiation beam at the system's isocenter. The radiation dose is delivered throughout the target volume in the breast by constantly moving the patient in a planned trajectory relative to the fixed isocenter. With this technique, the focal spot dynamically paints the dose distribution throughout the target volume in three dimensions.Dr. Jackson will conclude this symposium by describing the RSNA Quantitative Imaging Biomarkers Alliance (QIBA), which is funded in part by NIBIB and is a synergistic collaboration between medical physicists, radiologists, oncologists, industry representatives, and other stakeholders. The mission of QIBA is to improve the accuracy and practicality of quantitative image‐based biomarkers by increasing precision across devices, patients, and time, an essential step in incorporating quantitative imaging biomarkers into radiology practice. Validated quantitative imaging biomarkers are necessary to support precision medicine initiatives, multimodality / multiparametric applications in medicine, treatment planning and response assessment, and radiogenomics applications. Current applications in the QIBA portfolio extend to cancer diagnosis and treatment, pulmonary diseases, and neurological disorders.The overall goal of this symposium is to illustrate the bidirectional exchange between medical research and clinical practice. Revitalizing scientific excellence in clinical medical physics challenges practitioners to identify clinical limitations, which then drive research innovation; research funded by the NIH and other agencies develops technological solutions to these limitations, which are translated to the care environment to ultimately improve clinical practice in radiology and radiation oncology.
Recent observations show that small, young, stellar groupings of ~10 to 40 members tend of have a centrally-located most massive member, reminiscent of mass segregation seen in large clustered systems. Here, we analyze hydrodynamic simulations which form small clusters and analyze their properties in a manner identical to the observations. We find that the simulated clusters possess similar properties to the observed clusters, including a tendency to exhibit mass segregation. In the simulations, the central location of the most massive member is not due to dynamical evolution, since there is little interaction between the cluster members. Instead, the most massive cluster member appears to form at the center. We also find that the more massive stars in the cluster form at slightly earlier times.
The Doppler effect is commonly used to infer the velocity difference between stars based on the relative shifts in the rest-frame wavelengths of their spectral features. In dynamically-cold systems with a low velocity dispersion, such as wide binaries, loose star clusters, cold stellar streams or cosmological mini-halos, the scatter in the gravitational redshift from the surface of the constituent stars needs to be taken into account as well. Gravitational redshifts could be important for wide binaries composed of main sequence stars with separations >0.01 pc or in mini-halos with velocity dispersions <1 km/s. Variable redshift could also lead to a spurious "detection" of low-mass planets around a star with periodic photospheric radius variations.
Stavros Akras, Julio Ramirez-Velez, David Hiriart
et al.
We present optical (UBVRI) linear polarimetric observations of 8 Wolf-Rayet (WR) massive binaries and single stars. We have corrected the observed values for the interstellar extinction and polarization by the interstellar medium to obtain the intrinsic polarization and position angle. We find three highly polarization stars between 5% and 10% (WR1, WR5 and WR146), three between 3% and 4% (WR2, WR3 and WR4), and two between 1% and 2% (WR137 and WR140). Moreover, 5 stars show increasing degree of polarization to shorter wavelengths (e.g WR 146) indicative with asymmetric circumstellar envelope and 3 have nearly constant polarization within the errors (e.g WR 140).
We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex stellar system in the the Galactic bulge, known to have two populations at [Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide average [Fe/H]=-0.79 dex iron abundance and [alpha/Fe]=+0.36 dex enhancement. This new population extends the metallicity range of Terzan~5 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core collapse supernovae.
Eva Villaver, Arturo Manchado, Guillermo Garcia-Segura
We study the hydrodynamical behavior of the gas expelled by moving Asymptotic Giant Branch Stars interacting with the ISM. Our models follow the wind modulations prescribed by stellar evolution calculations, and we cover a range of expected relative velocities (10 to 100 km/s), ISM densities (between 0.01 and 1 cm-3), and stellar progenitor masses (1 and 3.5 Msun). We show how and when bow-shocks, and cometary-like structures form, and in which regime the shells are subject to instabilities. Finally, we analyze the results of the simulations in terms of the different kinematical stellar populations expected in the Galaxy.