Brackett Gamma Research Articles

A K-band spectral mini-survey of Galactic B[e] stars★

We present a mini-survey of Galactic B[e] stars mainly undertaken with the Large Binocular Telescope (LBT). B[e] stars show morphological features with hydrogen emission lines and an infrared excess, attributed to warm circumstellar dust. In general, these features are assumed to arise from dense, non-spherical, disk-forming circumstellar material in which molecules and dust can condensate. Due to the lack of reliable luminosities, the class of Galactic B[e] stars contains stars at very different stellar evolutionary phases like Herbig AeBe, supergiants or planetary nebulae. We took near-infrared long-slit K-band spectra for a sample of Galactic B[e] stars with the LBT-Luci I. Prominent spectral features, such as the Brackett gamma line and CO band heads are identified in the spectra. The analysis shows that the stars can be characterized as evolved objects. Among others we find one LBV candidate (MWC314), one supergiant B[e] candidate with 13CO (MWC137) and in two cases (MWC623 and AS 381) indications for the existence of a late-type binary companion, complementary to previous studies. For MWC84, IR spectra were taken at different epochs with LBT-Luci I and the GNIRS spectrograph at the Gemini North telescope. The new data show the disappearance of the circumstellar CO emission around this star, previously detectable over decades. Also no signs of a recent prominent eruption leading to the formation of new CO disk emission are found during 2010 and 2013.

EARLY-STAGE MASSIVE STAR FORMATION NEAR THE GALACTIC CENTER: Sgr C

We present near-infrared spectroscopy and 1 mm line and continuum observations of a recently identified site of high mass star formation likely to be located in the Central Molecular Zone near Sgr C. Located on the outskirts of the massive evolved HII region associated with Sgr C, the area is characterized by an Extended Green Object measuring ~10" in size (0.4 pc), whose observational characteristics suggest the presence of an embedded massive protostar driving an outflow. Our data confirm that early-stage star formation is taking place on the periphery of the Sgr C HII region, with detections of two protostellar cores and several knots of H2 and Brackett gamma emission alongside a previously detected compact radio source. We calculate the cores' joint mass to be ~10^3 Msun, with column densities of 1-2 x 10^24 cm-2. We show the host molecular cloud to hold ~10^5 Msun of gas and dust with temperatures and column densities favourable for massive star formation to occur, however, there is no evidence of star formation outside of the EGO, indicating that the cloud is predominantly quiescent. Given its mass, density, and temperature, the cloud is comparable to other remarkable non-star-forming clouds such as G0.253 in the Eastern CMZ.

Infrared identification of 2XMM J191043.4+091629.4

Here we report the infrared identification of the X-ray source 2XMM J191043.4+091629.4, which was detected by XMM-Newton/EPIC in the vicinity of the Galactic supernova remnant W49B. The aim of this work is to establish the nature of the X-ray source 2XMM J191043.4+091629.4 studying both the infrared photometry and spectroscopy of the companion. We analyse UKIDSS images around the best position of the X-ray source, and obtain spectra of the best candidate using NICS in the 3.5 m TNG telescope. We present both photometric and spectroscopic TNG analysis of the infrared counterpart of the X-ray source identifying emission lines in the K-band. H-band spectra does not present any significant feature. We have showed that Brackett gamma H I, at 2.165 micrometre, and He I, at 2.184 micrometre and at 2.058 micrometre, are present significantly in the infrared spectrum. The CO bands are also not present in our spectrum. Based on these results and the X-ray characteristics of the source we conclude that the infrared counterpart is an early B-type supergiant star with an E(B-V)= 7.6 +/- 0.3 at a distance of 16.0 +/- 0.5 kpc. This would be, therefore, the first high-mass X-ray binary in the Outer Arm at galactic longitudes between 30 and 60 degrees.

Neutral and ionised gas around the post-red supergiant IRC +10 420 at AU size scales

IRC +10420 is one of the few known massive stars in rapid transition from the Red Supergiant phase to the Wolf-Rayet or Luminous Blue Variable phase. The star has an ionised wind and using the Br gamma hydrogen recombination emission we assess the mass-loss on spatial scales of order 1 au. We present new VLT Interferometer AMBER data which are combined with all other AMBER data in the literature. The final dataset covers a position angle range of 180 degrees and baselines up to 110 meters. The spectrally dispersed visibilities, differential phases and line flux are conjointly analyzed and modelled. We also present AMBER/FINITO observations which cover a larger wavelength range and allow us to observe the Na I doublet at 2.2 micron. The data are complemented by X-Shooter data, which provide a higher spectral resolution view. The Brackett gamma line and the Na I doublet are both spatially resolved. After correcting the AMBER data for the fact that the lines are not spectrally resolved, we find that Br gamma traces a ring with a diameter of 4.18 milli-arcseconds. We consider a geometric model in which the Br gamma emission emerges from the top and bottom rings of an hour-glass shaped structure, viewed almost pole-on. It provides satisfactory fits to most visibilities and differential phases. The fact that we detect line emission from a neutral metal like Na I within the ionized region, a very unusual occurrence, suggests the presence of a dense pseudo-photosphere. The ionized wind can be reproduced with a polar wind, which could well have the shape of an hour-glass. The resolved Na I emission is found to occur on scales barely larger than the continuum. This fact and that many Yellow Hypergiants exhibit this comparatively rare emission hints at the presence of a "Yellow" or even "White Wall" in the Hertzsprung-Russell diagram, preventing them from visibly evolving to the blue.

INFRARED SPECTROSCOPY OF NEARBY RADIO ACTIVE ELLIPTICAL GALAXIES

In preparation for a study of their circumnuclear gas we have surveyed 60% of a complete sample of elliptical galaxies within 75 Mpc that are radiosources. Some 20% of our nuclear spectra have infrared emission lines, mostly Paschen lines, Brackett gamma and [FeII]. We consider the influence of radio power and black hole mass in relation to the spectra. Access to the spectra is provided as a community resource.

TIME-VARIABLE ACCRETION IN THE TW Hya STAR/DISK SYSTEM

We present two epochs of observations of TW Hya from the high-dispersion near-IR spectrograph ARIES at the MMT. We detect strong emission from the Brackett gamma transition of hydrogen, indicating an accretion rate substantially larger than previously estimated using hydrogen line emission. The Brackett gamma line-strength varies across our two observed epochs. We also measure circumstellar-to-stellar flux ratios (i.e., veilings) that appear close to zero in both epochs. These findings suggest that TW Hya experiences episodes of enhanced accretion while the inner disk remains largely devoid of dust. We discuss several physical mechanisms that may explain these observations.

SPATIALLY AND SPECTRALLY RESOLVED HYDROGEN GAS WITHIN 0.1 AU OF T TAURI AND HERBIG Ae/Be STARS

We present near-infrared observations of T Tauri and Herbig Ae/Be stars with a spatial resolution of a few milli-arcseconds and a spectral resolution of ~2000. Our observations spatially resolve gas and dust in the inner regions of protoplanetary disks, and spectrally resolve broad-linewidth emission from the Brackett gamma transition of hydrogen gas. We use the technique of spectro-astrometry to determine centroids of different velocity components of this gaseous emission at a precision orders of magnitude better than the angular resolution. In all sources, we find the gaseous emission to be more compact than or distributed on similar spatial scales to the dust emission. We attempt to fit the data with models including both dust and Brackett gamma-emitting gas, and we consider both disk and infall/outflow morphologies for the gaseous matter. In most cases where we can distinguish between these two models, the data show a preference for infall/outflow models. In all cases, our data appear consistent with the presence of some gas at stellocentric radii of ~0.01 AU. Our findings support the hypothesis that Brackett gamma emission generally traces magnetospherically driven accretion and/or outflows in young star/disk systems.

Interferometric science results on young stellar objects

Long-baseline interferometry at infrared wavelengths allows the innermost regions around young stars to be observed. These observations directly probe the location of the dust and gas in the disks. The characteristic sizes of these regions found are larger than previously thought. These results have motivated in part a new class of models of the inner disk structure, but the precise understanding of the origin of these low visibilities is still in debate. Mid-infrared observations probe disk emission over a larger range of scales revealing mineralogy gradients in the disk. Recent spectrally resolved observations allow the dust and gas to be studied separately showing that the Brackett gamma emission can find its origin either in a wind or in a magnetosphere and that there is probably no correlation between the location of the Brackett gamma emission and accretion. In a certain number of cases, the very high spatial resolution reveals very close companions and can determine their masses. Overall, these results provide essential information on the structure and the physical properties of close regions surrounding young stars especially where planet formation is suspected to occur.

Resolving the asymmetric inner wind region of the yellow hypergiant IRC +10420 with VLTI/AMBER in low and high spectral resolution mode

We obtained near-infrared long-baseline interferometry of IRC+10420 with the AMBER instrument of ESO's Very Large Telescope Interferometer (VLTI) in low and high spectral resolution (HR) mode to probe the photosphere and the innermost circumstellar environment of this rapidly evolving yellow hypergiant. In the HR observations, the visibilities show a noticeable drop across the Brackett gamma (BrG) line on all three baselines, and we found differential phases up to -25 degrees in the redshifted part of the BrG line and a non-zero closure phase close to the line center. The calibrated visibilities were corrected for AMBER's limited field-of-view to appropriately account for the flux contribution of IRC+10420's extended dust shell. We derived FWHM Gaussian sizes of 1.05 +/- 0.07 and 0.98 +/- 0.10 mas for IRC+10420's continuum-emitting region in the H and K bands, respectively, and the BrG-emitting region can be fitted with a geometric ring model with a diameter of 4.18 +0.19/-0.09 mas, which is approximately 4 times the stellar size. The geometric model also provides some evidence that the BrG line-emitting region is elongated towards a position angle of 36 degrees, well aligned with the symmetry axis of the outer reflection nebula. The HR observations were further analyzed by means of radiative transfer modeling using CMFGEN and the 2-D Busche & Hillier codes. Our spherical CMFGEN model poorly reproduces the observed line shape, blueshift, and extension, definitively showing that the IRC+10420 outflow is asymmetric. Our 2-D radiative transfer modeling shows that the blueshifted BrG emission and the shape of the visibility across the emission line can be explained with an asymmetric bipolar outflow with a high density contrast from pole to equator (8-16), where the redshifted light is substantially diminished.

Near-infrared studies of V1280 Sco (Nova Scorpii 2007)

We present spectroscopic and photometric results of Nova V1280 Sco which was discovered in outburst in early 2007 February. The large number of spectra obtained of the object leads to one of the most extensive, near-infrared spectral studies of a classical nova. The spectra evolve from a P-Cygni phase to an emission-line phase and at a later stage is dominated by emission from the dust that formed in this nova. A detailed model is computed to identify and study characteristics of the spectral lines. Inferences from the model address the vexing question of which novae have the ability to form dust. It is demonstrated, and strikingly corroborated with observations, that the presence of lines in the early spectra of low-ionization species like Na and Mg - indicative of low temperature conditions - appear to be reliable indicators that dust will form in the ejecta. It is theoretically expected that mass loss during a nova outburst is a sustained process. Spectroscopic evidence for such a sustained mass loss, obtained by tracing the evolution of a P-Cygni feature in the Brackett gamma line, is presented here allowing a lower limit of 25-27 days to be set for the mass-loss duration. Photometric data recording the nova's extended 12 day climb to peak brightness after discovery is used to establish an early fireball expansion and also show that the ejection began well before maximum brightness. The JHK light curves indicate the nova had a fairly strong second outburst around 100 days after the first.

Inner disk regions revealed by infrared interferometry

AbstractI review the results obtained by long-baseline interferometry at infrared wavelengths on the innermost regions around young stars. These observations directly probe the location of the dust and gas in the disks. The characteristic sizes of these regions are found larger than previously thought. These results have motivated in part a new class of models of the inner disk structure. However the precise understanding of the origin of these low visibilities is still in debate. Mid-infrared observations have probed disk emission over a larger range of scales revealing mineralogy gradients in the disk. Recent spectrally resolved observations allow the dust and gas to be studied separately. The few results show that the Brackett gamma emission can find its origin either in a wind or in a magnetosphere but there are no definitive answers yet. In a number of cases, the very high spatial resolution seems to reveal very close companions. In any case, these results provide crucial information on the structure and physical properties of disks surrounding young stars especially as initial conditions for planet formation.

Detection of knots and jets in IRAS 06061+2151

We report detection of a Young Stellar Object with an evidence for an outflow in the form of knots in the molecular hydrogen emission line (2.121 micron) towards the massive star forming region IRAS 06061+2151. Near-infrared images reveal IRAS 06061+2151 to be a cluster of at least five sources, four of which seem to be early B type young stellar objects, in a region of 12 arcsec surrounded by a nebulosity. The presence of the knots that are probably similar to the HH objects in the optical wavelengths, suggests emerging jets from one of the cluster members. These jets appear to excite a pair of knot-like objects (Knot-NW and Knot-SE) and extend over a projected size of 0.5pc. The driving source for the jets is traced back to a member of the cluster whose position in the H-Ks/J-H color-color diagram indicates that it is a Class 1 type pre-mainsequence star. We also obtained K band spectra of the brightest source in the cluster and of the nearby nebular matter. The spectra show molecular hydrogen emission lines but do not show Brackett gamma line at 2.167 micron. These spectra suggest that the excitation of the molecular hydrogen lines is probably due to a mild shock.

56Ni dredge-up in the type IIp supernova 1995V

We present contemporary infrared and optical spectra of the plateau type II SN 1995V in NGC 1087 covering four epochs, approximately 22 to 84 days after shock breakout. The data show, for the first time, the infrared spectroscopic evolution during the plateau phase of a typical type II event. In the optical region P Cygni lines of the Balmer series and of metals lines were identified. The infrared (IR) spectra were largely dominated by the continuum, but P Cygni Paschen lines and Brackett gamma lines were also clearly seen. The other prominent IR features are confined to wavelengths blueward of 11000 \AA and include Sr II 10327, Fe II 10547, C I 10695 and He I 10830 \AA. We demonstrate the presence of He I 10830 \AA on days 69 and 85. The presence of this line at such late times implies re-ionisation. A likely re-ionising mechanism is gamma-ray deposition following the radioactive decay of 56Ni. We examine this mechanism by constructing a spectral model for the He I 10830 \AA line based on explosion model s15s7b2f of Weaver & Woosley (1993). We find that this does not generate the observed line owing to the confinement of the 56Ni to the central zones of the ejecta. In order to reproduce the He I line, it was necessary to introduce additional upward mixing of the 56Ni, with 10^{-5} of the total nickel mass reaching above the helium photosphere. In addition, we argue that the He I line-formation region is likely to have been in the form of pure helium clumps in the hydrogen envelope.

Infrared Observations of G0.18−0.04

The Galactic Center H(II) region, G0.18-0.04, the 'Sickle', is located where the nonthermal 'Arc' crosses the Galactic plane. The Sickle appears to be the ionized edge of a dense molecular cloud. The source of ionization has been ascribed to both the interaction of the cloud with the magnetic field of the Arc and to the hot stars in the adjacent cluster, AFGL 2004, also known as the 'Quintuplet Cluster'. This paper addresses the relative locations of the stars, the ionized and molecular gas, and the sources of gas excitation and dust heating. Using NASA's Kuiper Airborne Observatory, we have observed the far infrared forbidden lines of [S(III)] 18.7 and 33.5 micrometers, [Si(II)] 34.8 micrometers, [Ne(III)] 36.0 micrometers, [O(III)] 51.8 and 88.4 micrometers, [N(III)] 57.3 micrometers, [O(II)] 63.2 and 146 micrometers, [C(II)] 158 micrometers, and [N(II)] 205 micrometers and the adjacent continua at 11 positions around G0.18-0.04, including G0.15-0.05, the 'Pistol', in a beamsize of 40 - 60 arcsec. The electron density, the ionic abundances, and the ionization structure of the H(II) region are estimated from the doubly ionized line fluxes. The density and radiation field found in the photodissociation region (PDR) between the H(II) region and the molecular cloud are estimated from the [C(II)] and [O(I)] line fluxes and the far-infrared continuum. We compare the ionization structure and the PDR properties to shell models of H(II) regions with varying distances from their exciting stars. The agreement of observations and models indicates that the hot stars of AFGL 2004 are the likely source of ionization of the Sickle. Additional hot stars are necessary to ionize the more outlying positions. However, because of its low ionization and high PDR radiation field, the Pistol cannot be as close to AFGL 2004 as indicated by its close proximity on the sky. Instead, the Pistol is probably ionized by the luminous blue variable candidate, Pistol Source A. We estimated the extinction to the region from the distribution of the J, H, and K' magnitudes of the stars in the field that we measured from the Anglo-Australian telescope and from the IRAS LRS spectrum of AFGL 2004. The extinction is fairly uniform, with no enhancement from the molecular cloud. The strength of Brackett gamma, the 19-micrometer lines and continuum, and the IRAS 25-micrometer continuum are all consistent with the absence of a dense, foreground molecular cloud. We conclude that the H(II) region is on the near side of the dense cloud.

The luminous starburst galaxy UGC 8387

We present broad-band J, H, and K images and K-band spectroscopy of the luminous starburst galaxy UGC 8387. The images show a disturbed morphology, tidal tails, and a single elognated nucleus. Near infrared color maps constructed from the images reveal that the nucleus region is highly reddened. Strong emission from the central 3 arcseconds in the 2.166 micrometer Brackett gamma, 2.122 micrometer H2 v = 1-0 S(1), and 2.058 micrometer He I lines is present in the K-band spectrum. From the Brackett gamma and published radio fluxes, we find an optical depth toward the nucleus of tau(sub V) approximately 24. The CO band heads produce strong absorption in the spectral region long-ward of 2.3 micrometers. We measure a 'raw' CO index of 0.17 +/- 0.02 mag, consistent with a population of K2 supergiants of K4 giants. The nuclear colors, however, are not consistent with an obscured population of evolved stars. Instead, the red colors are best explained by an obscured mixture of stellar and warm dust emission. The amount of dust emission predicted by the near-infrared colors exceeds that expected from comparisons to galactic H II regions. After correcting the spectrum of UGC 8387 for dust emission and extinction, we obtain a CO index of greater than or equal to 0.25 mag. This value suggests the stellar component of the 2.2 micrometer light is dominated by young supergiants. The infrared excess, L(sub IR)/L(sub Ly alpha) derived for UGC 8387 is lower than that observed in galactic H II regions and M82. This implies that either the lower or upper mass cutoff of the initial mass function must be higher than those of local star-forming regions and M82. The intense nuclear starburst in this galaxy is presumably the result of merger activity; and we estimate the starburst age to be at least a few times 10(exp 7) yr.

The He i 2.06 Micron to Brackett gamma Ratio as a Nebular Diagnostic

The strength of the He I 2.06 μm emission line relative to hydrogen recombination features has been previously proposed as a diagnostic of effective temperature T eff for stars powering H II regions. Such an indicator would be of particular interest for constraining the high-end initial mass function in starbursts. I reexamine the sensitivity of the 2.06 μm feature to nebular conditions, and find that constraints on the ionizing continuum shape are difficult to determine in the absence of additional constraints on nebular properties

Optically thick infrared CO emission in WL 16

view Abstract Citations (12) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optically Thick Infrared CO Emission in WL 16 Thompson, Rodger I. ; Jannuzi, Buell T. Abstract Reanalysis of the NIR spectrum of the star-formation object WL 16 indicates that the observed infrared CO emission has a high optical depth, creating a CO emission continuum feature. A new extinction value A(v) = 40 places the Brackett gamma emission within the normal range for low-luminosity line excess sources. The observations are consistent with a spherical cooling outflow with the infrared CO and hydrogen emission arising from physically separate regions. Other geometries are not excluded by the observations. Publication: The Astrophysical Journal Pub Date: September 1989 DOI: 10.1086/167845 Bibcode: 1989ApJ...344..799T Keywords: Carbon Monoxide; Emission Spectra; Infrared Sources (Astronomy); Star Formation; Interstellar Gas; Optical Thickness; Astrophysics; INFRARED: SPECTRA; INTERSTELLAR: MOLECULES; NEBULAE: INDIVIDUAL NAME: RHO OPHIUCHI; STARS: FORMATION full text sources ADS | data products SIMBAD (2)

Fabry-Perot Images of Ionised and Molecular Hydrogen in Sgr A

Images of the central 36 arcseconds of the Galaxy in the Brackett gamma line of atomic hydrogen (2.17μm) at a spatial resolution of 0.6 arcsec and a velocity resolution of 110 km/sec were obtained using UKIRT. The velocity separation between adjacent frames is 55 km/sec; 17 different velocities channels were imaged. Several distinct kinematic components are evident within the clumpy distribution of the ionised gas. An image in the v=1-0 S(1) line of molecular hydrogen (2.12μm) clearly resolves the structure of the “molecular ring.”

2.0 to 2.4 micron spectroscopy of T Tauri stars

Velocity-resolved 2.0-2.5-micron observations of the T Tau stars T, DF, DG, DK, HL, and RY Tau, SU Aur, and GW Ori are presented. For each of these stars except SU Aur, the Brackett gamma line was detected in emission with line widths inthe range of about 130-230 km/s. The Brackett gamma line profile of SU Aur is complex, having components of both emission and absorption. The first measurement of CO band-head emission in DG Tau is reported, and it is shown that published radio continuum fluxes of young stars far exceed what could be produced in an envelope ionized by only the stellar photospheric Lyman continuum. The excess of radio emission is found to be much greater in low-luminosity sources (e.g., the T Tau stars). 54 references.

Velocity resolved spectroscopy of the Brackett gamma line emission of CRL 490 and M17 IRS 1

view Abstract Citations (72) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Velocity resolved spectroscopy of the brackett gamma line emission ofCRL 490 and M 17 IRS 1. Simon, M. ; Righini-Cohen, G. ; Fischer, J. ; Cassar, L. Abstract High-resolution spectra of the Br-gamma lines of CRL 490 and M17 IRS 1 are presented, which give evidence for strong gas flows in the ionized regions associated with the objects. The Br-gamma line of CRL 490 is about 150 km/s wide at half-power, and is blueshifted by about 30 km/s with respect to the CO velocity of the surrounding molecular cloud. The Br-gamma line of M17 IRS 1 is about 135 km/s wide at half-power, and is blueshifted by about 24 km/s with respect to its molecular cloud. Mass loss rates appear to exceed 10 to the -7th solar mass per year, and modeling of the profiles shows that the Br-gamma lines are probably optically thick, which implies that estimates of the dust extinction to these objects on the basis of nebular recombination theory are invalid. Publication: The Astrophysical Journal Pub Date: December 1981 DOI: 10.1086/159497 Bibcode: 1981ApJ...251..552S Keywords: Astronomical Spectroscopy; Emission Spectra; Gamma Ray Spectra; Infrared Spectra; Nebulae; Spectral Line Width; Gas Flow; High Resolution; Ionized Gases; Line Spectra; Molecular Spectra; Optical Thickness; Spectral Resolution; Astrophysics full text sources ADS | data products SIMBAD (2)