scholarly journals Radio Molecular Line Observations of Late Type Stars

1977 ◽  
Vol 42 ◽  
pp. 495-520 ◽  
Author(s):  
A. Winnberg
Keyword(s):  
Near Infrared ◽  
Spectral Lines ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Long Baseline ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Opening Up ◽  
Excellent Tool ◽  
Geometry And Kinematics

Radio observations of spectral lines from OH, H2O, SiO and CO have put the spot-light on late-type stars and revived the interest in them. Especially they have helped the understanding of the outer envelopes of these stars and of their mass loss. They also have revealed late-type stars that are hidden from observation at optical and near-infrared wavelengths by their dense surrounding shells of gas and dust. The strong maser lines from OH, H2O and SiO have additionally given us an excellent tool in mapping the distribution of late-type variables throughout the Galaxy. On the other hand, the interpretation of the maser amplified lines in terms of a model is difficult. Very-long-baseline interferometry (VLBI) of these lines might be a way of studying the geometry and kinematics of the envelopes but there are a few problems connected with these observations which I will point out in this paper. However, recently “thermal” microwave lines of SiO and CO have been observed from late-type stars. These lines might be easier to interpret regarding physical processes in the outer circumstellar envelopes. As so often when a new field is opening up in astronomy the solutions to several old problems have been found but at the same time many more new problems have been brought up.

scholarly journals Effects of fast rotation on the wind of Luminous Blue Variables

2010 ◽  
Vol 6 (S272) ◽  
pp. 56-61
Author(s):  
Jose H. Groh
Keyword(s):  
Near Infrared ◽  
Rotational Velocity ◽  
Spectral Lines ◽  
High Resolution Spectroscopy ◽  
Luminous Blue Variables ◽  
Eta Carinae ◽  
Fast Rotation ◽  
Long Baseline ◽  
Infrared Interferometry ◽  
Fast Rotating

AbstractWhile theoretical studies have long suggested a fast-rotating nature of Luminous Blue Variables (LBVs), observational confirmation of fast rotation was not detected until recently. Here I discuss the diagnostics that have allowed us to constrain the rotational velocity of LBVs: broadening of spectral lines and latitude-dependent variations of the wind density structure. While rotational broadening can be directly detected using high-resolution spectroscopy, long-baseline near-infrared interferometry is needed to directly measure the shape of the latitude-dependent photosphere that forms in a fast-rotating star. In addition, complex 2-D radiative transfer models need to be employed if one's goal is to constrain rotational velocities of LBVs. Here I illustrate how the above methods were able to constrain the rotational velocities of the LBVs AG Carinae, HR Carinae, and Eta Carinae.

scholarly journals Milky Way demographics with the VVV survey

2018 ◽  
Vol 619 ◽  
pp. A4 ◽  
Author(s):  
Javier Alonso-García ◽  
Roberto K. Saito ◽  
Maren Hempel ◽  
Dante Minniti ◽  
Joyce Pullen ◽  
...  
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Stellar Populations ◽  
Wide Field ◽  
Public Survey ◽  
Wide Field Of View ◽  
Spread Function ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Galactic Stellar Populations

Context. The inner regions of the Galaxy are severely affected by extinction, which limits our capability to study the stellar populations present there. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey has observed this zone at near-infrared wavelengths where reddening is highly diminished. Aims. By exploiting the high resolution and wide field-of-view of the VVV images we aim to produce a deep, homogeneous, and highly complete database of sources that cover the innermost regions of our Galaxy. Methods. To better deal with the high crowding in the surveyed areas, we have used point spread function (PSF)-fitting techniques to obtain a new photometry of the VVV images, in the ZY JHKs near-infrared filters available. Results. Our final catalogs contain close to one billion sources, with precise photometry in up to five near-infrared filters, and they are already being used to provide an unprecedented view of the inner Galactic stellar populations. We make these catalogs publicly available to the community. Our catalogs allow us to build the VVV giga-CMD, a series of color-magnitude diagrams of the inner regions of the Milky Way presented as supplementary videos. We provide a qualitative analysis of some representative CMDs of the inner regions of the Galaxy, and briefly mention some of the studies we have developed with this new dataset so far.

scholarly journals Magnification and evolution biases in large-scale structure surveys

2021 ◽  
Vol 2021 (12) ◽  
pp. 009
Author(s):  
Roy Maartens ◽  
José Fonseca ◽  
Stefano Camera ◽  
Sheean Jolicoeur ◽  
Jan-Albert Viljoen ◽  
...  
Keyword(s):  
Luminosity Function ◽  
Large Scale ◽  
Near Infrared ◽  
Physical Change ◽  
Number Density ◽  
Galaxy Surveys ◽  
Intensity Mapping ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Derivatives Of

Abstract Measurements of galaxy clustering in upcoming surveys such as those planned for the Euclid and Roman satellites, and the SKA Observatory, will be sensitive to distortions from lensing magnification and Doppler effects, beyond the standard redshift-space distortions. The amplitude of these contributions depends sensitively on magnification bias and evolution bias in the galaxy number density. Magnification bias quantifies the change in the observed number of galaxies gained or lost by lensing magnification, while evolution bias quantifies the physical change in the galaxy number density relative to the conserved case. These biases are given by derivatives of the number density, and consequently are very sensitive to the form of the luminosity function. We give a careful derivation of the magnification and evolution biases, clarifying a number of results in the literature. We then examine the biases for a variety of surveys, encompassing galaxy surveys and line intensity mapping at radio and optical/near-infrared wavelengths.

scholarly journals The Luminosity of the Central Parsec of the Galaxy

1989 ◽  
Vol 136 ◽  
pp. 423-436
Author(s):  
M. W. Werner ◽  
J. A. Davidson
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Thermal Emission ◽  
Large Magellanic Cloud ◽  
Infrared Emission ◽  
Infrared Observations ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Central Parsec ◽  
30 Doradus

The luminosity of the central 5 pc of the Galaxy -encompassing the inner regions of the rotating ring of dust and gas which surrounds the galactic center - emerges primarily at infrared wavelengths in the form of thermal emission from heated dust. The nature and location of the sources which heat the dust can be inferred from the spatial and temperature distribution of the thermal infrared emission (λ>20um), from studies of the ionized gas in this region, and from direct imaging in the near infrared. These observations show that the principal heating sources within this 5-pc region are concentrated within the central parsec of the Galaxy and indicate that the luminosity of these sources is within a factor of two of 107 LO. The near-infrared observations of the compact sources at the galactic center do not reveal a single dominant source but suggest instead that the several components of the IRS-16 complex, taken together, may contribute the bulk of the luminosity; however, the data also permit a single object to dominate the energetics of this region. We draw attention to the striking morphological similarities between the galactic center and the innermost regions of the 30 Doradus nebula in the Large Magellanic Cloud and speculate that the luminosity sources in the galactic center may resemble the early-type supergiants in 30 Doradus.

scholarly journals Low-Luminosity Stars: Past and Future

1998 ◽  
Vol 11 (1) ◽  
pp. 433-434
Author(s):  
I.N. Reid
Keyword(s):  
Near Infrared ◽  
Effective Means ◽  
Brown Dwarfs ◽  
Current Theory ◽  
Brown Dwarf ◽  
Wide Range ◽  
Grain Formation ◽  
The Galaxy ◽  
First Results ◽  
Infrared Wavelengths

The expression “low luminosity stars” is a descriptive category which spans a wide range of objects, from the oldest stellar remnants in the Galaxy (Wood) through failed stars (Jones, Gould) to the enigmatic MACHOs, discernible not in themselves but only through their effects on others (Bennet). All of these have attracted considerable attention in recent years, and significant progress has been achieved in each case, even if our understanding has failed to keep up with observations. However, it is in the area of brown dwarfs where the most dramatic results have been obtained. The existence of such objects has been predicted theoretically for well over thirty years, but predictions can fail. Thus the discovery of G1229B (Nakajima et al, 1995), an unambiguous substellar-mass object, followed by the detection of lithium in Teide 1 and Calar 3 in the Pleiades (Rebolo et al, 1996) mark a turning point in studies of brown dwarfs. The issue now is not whether they exist, but what are their properties as a class. With that in mind, a number of obvious questions arise. First, what is the most effective method of finding brown dwarfs? Both brown dwarfs and VLM stars have effective temperatures below 2500K. Hence, many surveys concentrated on searching for objects which were very red at near-infrared wavelengths, and the blue JHK colours exhibited by Gl 229B cameas something of a surprise. This should not have been the case, of course, since Tsuji (1964) predicted the presence of methane in such cool atmospheres well before the term ’brown dwarf’ was invented. Current theory, as summarised in these sessions by Tsuji and Burrows, predicts that, as one moves to lower temperatures, grain formation initially drives (J-K) redward, before grains settle below τ ~ 1 and CH4 absorption sets in. Throughout, however, the optical-to-IR colours, straddling the peak in the emergent flux distribution, become progressively redder (Reid, 1994). Those colours therefore offer the most effective means of identifying both GD 165B-like and Gl 229B-like sources - an argument reinforced by the first results from the IJK DENIS survey (Delfosse et al, 1997).

scholarly journals Observations of the near infrared survace brightness distribution of the galaxy

1979 ◽  
Vol 84 ◽  
pp. 377-380 ◽  
Author(s):  
H. Okuda ◽  
T. Maihara ◽  
N. Oda ◽  
T. Sugiyama
Keyword(s):  
Central Region ◽  
Near Infrared ◽  
Interstellar Extinction ◽  
Brightness Distribution ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Optical Wavelengths ◽  
Inner Region ◽  
Infrared Brightness

Studies of the stellar distribution in the inner region of our Galaxy have been seriously hampered at optical wavelengths by strong interstellar extinction. The extinction decreases considerably at infrared wavelengths, allowing us to look deep into the Galaxy. Motivated by this, we have tried to observe the near infrared brightness distribution of the central region of the Galaxy (Okuda et al., 1977, Maihara et al., 1978, Oda et al., 1978). Similar observations have been carried out by Hayakawa et al., (1976), Ito et al., (1977), and Hofmann et al., (1977). These observations have provided valuable information on the distributions of stars and dust in the inner Galaxy (Hayakawa et al., 1977, Maihara et al., 1978, Oda et al., 1978).

scholarly journals Circumstellar envelopes of Cepheids: a possible bias affecting the distance scale?

2012 ◽  
Vol 8 (S289) ◽  
pp. 157-160 ◽  
Author(s):  
Pierre Kervella ◽  
Alexandre Gallenne ◽  
Antoine Mérand
Keyword(s):  
Near Infrared ◽  
Thermal Infrared ◽  
Distance Scale ◽  
Pulsation Period ◽  
Circumstellar Envelopes ◽  
Long Period ◽  
Long Baseline ◽  
Potential Impact ◽  
Visible Wavelengths ◽  
The Impact

AbstractCircumstellar envelopes (CSEs) have been detected around many Cepheids, first based on long-baseline interferometry, and now also using other observing techniques. These envelopes are particularly interesting for two reasons: their presence could impact the Cepheid distance scale, and they may be valuable tracers of stellar mass loss. Here we focus on their potential impact on the calibration of the Cepheid distance scale. We consider the photometric contribution of the envelopes in the visible, near-, and thermal-infrared domains. We conclude that the impact of CSEs on the apparent luminosities of Cepheids is negligible at visible wavelengths and generally weak (<5%) in the near-infrared (λ ≈ 2 μm). In the thermal-infrared domain (λ ≈ 8 μm), the flux contribution of the CSEs differs depending on the pulsation period: it is relatively weak (<15%) for stars with periods shorter than P ≈ 10 days, but can reach ≈ 30% for long-period Cepheids. We specifically discuss the long-period Galactic Cepheid RS Puppis, which exhibits a very large circumstellar, dusty envelope, and we conclude that this is not a representative case. Overall, the contribution of CSEs to the usual period–luminosity relations (from the visible to the K band) is mostly negligible. They could affect calibrations at longer wavelengths, although the presence of envelopes may have been partially taken into account in the existing empirical calibrations.

scholarly journals ALHAMBRA survey: morphological classification

2012 ◽  
Vol 10 (H16) ◽  
pp. 378-378
Author(s):  
M. Pović ◽  
M. Huertas-Company ◽  
I. Márquez ◽  
J. Masegosa ◽  
J. A. López Aguerri ◽  
...  
Keyword(s):  
Near Infrared ◽  
High Redshift ◽  
Morphological Properties ◽  
Support Vector ◽  
Late Type ◽  
Morphological Classification ◽  
Photometric Redshifts ◽  
Photometric Redshift ◽  
The Galaxy ◽  
Medium Band

AbstractThe Advanced Large Homogeneous Area Medium Band Redshift Astronomical (ALHAMBRA) survey is a photometric survey designed to study systematically cosmic evolution and cosmic variance (Moles et al.2008). It employs 20 continuous medium-band filters (3500 - 9700 Å), plus JHK near-infrared (NIR) bands, which enable measurements of photometric redshifts with good accuracy. ALHAMBRA covers > 4 deg2 in eight discontinuous regions (~ 0.5 deg2 per region), of theseseven fields overlap with other extragalactic, multiwavelength surveys (DEEP2, SDSS, COSMOS, HDF-N, Groth, ELAIS-N1). We detect > 600.000 sources, reaching the depth of R(AB) ~ 25.0, and photometric accuracy of 2-4% (Husillos et al., in prep.). Photometric redshifts are measured using the Bayesian Photometric Redshift (BPZ) code (Benítez et al.2000), reaching one of the best accuracies up to date of δz/z ≤ 1.2% (Molino et al., in prep.).To deal with the morphological classification of galaxies in the ALHAMBRA survey (Pović et al., in prep.), we used the galaxy Support Vector Machine code (galSVM; Huertas-Company 2008, 2009), one of the new non-parametric methods for morphological classification, specially useful when dealing with low resolution and high-redshift data. To test the accuracy of our morphological classification we used a sample of 3000 local, visually classified galaxies (Nair & Abraham 2010), moving them to conditions typical of our ALHAMBRA data (taking into account the background, redshift and magnitude distributions, etc.), and measuring their morphology using galSVM. Finally, we measured the morphology of ALHAMBRA galaxies, obtaining for each source seven morphological parameters (two concentration indexes, asymmetry, Gini, M20 moment of light, smoothness, and elongation), probability if the source belongs to early- or late-type, and its error. Comparing ALHAMBRA morph COSMOS/ACS morphology (obtained with the same method) we expect to have qualitative separation in two main morphological types for ~ 20.000 sources in 8 ALHAMBRA fields. For early-type galaxies we expect to recover ~ 70% and 30-40% up to magnitudes 20.0 and 21.5, respectively, having the contamination of late-types of < 7%. For late-type galaxies, we expect to recover ~ 70%, 60 - 70%, and ~ 30% of sources up to magnitudes 22.0, 22.5, and 23.0, respectively, having the contamination of early-types of ≤ 10%. These data will be used to study the evolution of active and non-active galaxies respect to morphology and morphological properties of galaxies in groups and clusters.

scholarly journals Round Table Summary: Stellar Interferometry as a Tool to Investigate Atmospheres and to Compare Observations with Models

2003 ◽  
Vol 210 ◽  
pp. 313-321
Author(s):  
Markus Wittkowski
Keyword(s):  
Near Infrared ◽  
Round Table ◽  
Stellar Atmosphere ◽  
Stellar Model ◽  
Stellar Atmospheres ◽  
Stellar Spectra ◽  
Long Baseline ◽  
Stellar Interferometry ◽  
Infrared Wavelengths ◽  
Spectrally Resolved

Long-baseline interferometry at optical and near-infrared wavelengths is an emerging technology which is quickly becoming a useful tool to investigate stellar atmospheres and to compare observations with models. Stellar atmosphere models have so far mainly been constrained by comparisons with stellar spectra which are integrated over the stellar disks. Interferometric observations provide spatially and spectrally resolved information and can thus provide important complementary observational information which can be compared to model predictions. Here, I summarize the different aspects on this topic which were discussed at a round table on Thursday, June 20, 2002, during IAU Symposium 210. This summary gives an overview on discussed interferometric facilities and techniques, concepts to study atmospheres by optical interferometry, and particular classes of objects. We conclude that more frequent interactions between the efforts of atmosphere modelling and interferometric observations promise to lead to increased confidence in stellar model atmospheres and to further advancement of the field in the next years.

scholarly journals Electromechanically reconfigurable optical nano-kirigami

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shanshan Chen ◽  
Zhiguang Liu ◽  
Huifeng Du ◽  
Chengchun Tang ◽  
Chang-Yin Ji ◽  
...  
Keyword(s):  
Near Infrared ◽  
Large Range ◽  
Three Dimensional ◽  
High Contrast ◽  
Si Substrate ◽  
High Modulation ◽  
Gold Nanostructure ◽  
Infrared Wavelengths ◽  
On Chip ◽  
Nano Electromechanical System

AbstractKirigami, with facile and automated fashion of three-dimensional (3D) transformations, offers an unconventional approach for realizing cutting-edge optical nano-electromechanical systems. Here, we demonstrate an on-chip and electromechanically reconfigurable nano-kirigami with optical functionalities. The nano-electromechanical system is built on an Au/SiO2/Si substrate and operated via attractive electrostatic forces between the top gold nanostructure and bottom silicon substrate. Large-range nano-kirigami like 3D deformations are clearly observed and reversibly engineered, with scalable pitch size down to 0.975 μm. Broadband nonresonant and narrowband resonant optical reconfigurations are achieved at visible and near-infrared wavelengths, respectively, with a high modulation contrast up to 494%. On-chip modulation of optical helicity is further demonstrated in submicron nano-kirigami at near-infrared wavelengths. Such small-size and high-contrast reconfigurable optical nano-kirigami provides advanced methodologies and platforms for versatile on-chip manipulation of light at nanoscale.

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