HI Recombination Lines Research Articles

MINDS: Mid-infrared atomic and molecular hydrogen lines in the inner disk around a low-mass star

Context. Understanding the physical conditions of circumstellar material around young stars is crucial to star and planet formation studies. In particular, very low-mass stars (M★ < 0.2 M⊙) are interesting sources to characterize as they are known to host a diverse population of rocky planets. Molecular and atomic hydrogen lines can probe the properties of the circumstellar gas. Aims. This work aims to measure the mass accretion rate, the accretion luminosity, and more generally the physical conditions of the warm emitting gas in the inner disk of the very low-mass star 2MASS-J16053215-1933159. We investigate the source mid-infrared spectrum for atomic and molecular hydrogen line emission. Methods. We present the full James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) spectrum of the protoplanetary disk around the very low-mass star 2MASS-J16053215-1933159 from the MINDS GTO program, previously shown to be abundant in hydrocarbon molecules. We analyzed the atomic and molecular hydrogen lines in this source by fitting one or multiple Gaussian profiles. We then built a rotational diagram for the H2 lines to constrain the rotational temperature and column density of the gas. Finally, we compared the observed atomic line fluxes to predictions from two standard emission models. Results. We identify five molecular hydrogen pure rotational lines and 16 atomic hydrogen recombination lines in the 5–20 µm spectral range. The spectrum indicates optically thin emission for both species. We use the molecular hydrogen lines to constrain the mass and temperature of the warm emitting gas. We derive a total gas mass of only 2.3 × 10−5 MJup and a temperature of 635 K for the warm H2 gas component located in the very inner disk (r < 0.033 au), which only accounts for a small fraction of the upper limit for the disk mass from continuum observations (0.2 MJup). The HI (7−6) recombination line is used to measure the mass accretion rate (4.0 × 10−10 M⊙ yr−1) and luminosity (3.1 × 10−3 L⊙) onto the central source. This line falls close to the HI (11−8) line, however at the spectral resolution of JWST MIRI we managed to measure both separately. Previous studies based on Spitzer have measured the combined flux of both lines to measure accretion rates. HI recombination lines can also be used to derive the physical properties of the gas using atomic recombination models. The model predictions of the atomic line relative intensities constrain the atomic hydrogen density to about 109−1010 cm−3 and temperatures up to 5000 K. Conclusions. The JWST-MIRI MRS observations for the very low-mass star 2MASS-J16053215-1933159 reveal a large number of emission lines, many originating from atomic and molecular hydrogen because we are able to look into the disk warm molecular layer. Their analysis constrains the physical properties of the emitting gas and showcases the potential of JWST to deepen our understanding of the physical and chemical structure of protoplanetary disks.

JWST Observations of Young protoStars (JOYS)

Context. Accretion and ejection dictate the outcomes of star and planet formation processes. The mid-infrared (MIR) wavelength range offers key tracers of processes that have been difficult to detect and spatially resolve in protostars until now. Aims. We aim to characterize the interplay between accretion and ejection in the low-mass Class I protobinary system TMC1, comprising two young stellar objects: TMC1-W and TMC1-E at a 85 au separation. Methods. Using the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) observations in 5–28 μm range, we measured the intensities of emission lines of H2, atoms, and ions, for instance, the [Fe II] and [Ne II], and HI recombination lines. We analyzed the spatial distribution of the different species using the MIRI Medium Resolution Spectrometer (MRS) capabilities to spatially resolve emission at 0″​​.2–0″​​.7 scales. we compared these results with the corresponding Atacama Large Millimeter/submillimeter Array (ALMA) maps tracing cold gas and dust. Results. We detected H2 outflow coming from TMC1-E, with no significant H2 emission from TMC1-W. The H2 emission from TMC1-E outflow appears narrow and extends to wider opening angles with decreasing Eup from S(8) to S(1) rotational transitions, indicating the disk wind as its origin. The outflow from TMC1-E protostar shows spatially extended emission lines of [Ne II], [Ne III], [Ar II], and [Ar III], with their line ratios consistent with UV radiation as a source of ionization. With ALMA, we detected an accretion streamer infalling from > 1000 au scales onto the TMC1-E component. The TMC1-W protostar powers a collimated jet, detected with [Fe II] and [Ni II], making it consistent with energetic flow. A much weaker ionized jet is observed from TMC1-E, and both jets appear strikingly parallel to each other, indicating that the disks are co-planar. TMC1-W is associated with strong emission from hydrogen recombination lines, tracing the accretion onto the young star. Conclusions. MIRI-MRS observations provide an unprecedented view of protostellar accretion and ejection processes on 20 au scales. Observations of a binary Class I protostellar system show that the two processes are clearly intertwined, with accretion from the envelope onto the disk influencing a wide-angle wind ejected on disk scales. Finally, the accretion from the protostellar disk onto the protostar is associated with the source launching a collimated high-velocity jet within the innermost regions of the disk.

Herschel Planetary Nebula Survey (HerPlaNS)★: hydrogen recombination laser lines in Mz 3

The bipolar nebula Menzel 3 (Mz 3) was observed as part of the \textit{Herschel} Planetary Nebula Survey (\textit{HerPlaNS}), which used the PACS and SPIRE instruments aboard the \textit{Herschel Space Observatory} to study a sample of planetary nebulae (PNe). In this paper, one of the series describing \textit{HerPlaNS} results, we report the detection of H I recombination lines (HRLs) in the spectrum of Mz 3. Inspection of the spectrum reveals the presence of 12 HRLs in the 55 to 680 $\mu$m range covered by the PACS and SPIRE instruments (H11$\alpha$ to H21$\alpha$ and H14$\beta$). The presence of HRLs in this range is unusual for PNe and has not been reported in Mz 3 before. Our analysis indicates that the HRLs we observed are enhanced by laser effect occurring in the core of Mz 3. Our arguments for this are: (i) the available Mz 3 optical to submillimetre HRL $\alpha$ line intensity ratios are not well reproduced by the spontaneous emission of optically thin ionized gas, as would be typical for nebular gas in PNe; (ii) the compact core of Mz 3 is responsible for a large fraction of the Herschel HRLs emission; (iii) the line intensity ratios for Mz 3 are very similar to those in the core emission of the well known star MWC 349A, where laser effect is responsible for the enhancement of HRLs in the Herschel wavelength range; (iv) the physical characteristics relevant to cause laser effect in the core of MWC 349A are very similar to those in the core of Mz 3.

Interpreting the simultaneous variability of near-IR continuum and line emission in young stellar objects

We present new near-infrared (IR) spectra (0.80-1.35um) of the pre-Main Sequence source PV Cep taken during a monitoring program of eruptive variables we are conducting since some years. Simultaneous photometric and spectroscopic observations are systematically carried out during outburst and quiescence periods. By correlating extinction-free parameters, such as HI recombination lines and underlying continuum, it is possible to infer on the mechanism(s) responsible for their origin. Accretion and mass loss processes have a dominant role in determining the PV Cep irregular variability of both continuum and line emission. The potentialities of the observational modality are also discussed.

Ring-like features around young B stars

<i>Aims. <i/>We investigate the nature of two young intermediate mass stars namely IRAS20293+3952 (I20293) and IRAS05358+3843 (I05358), which display clearly defined H<sub>2<sub/> emission rings.<i>Methods. <i/>High resolution deconvolution of finely sampled 3.6–8.0 <i>μ<i/>m Spitzer-IRAC images are carried out. Continuum-subtracted 2.122 <i>μ<i/>m H<sub>2<sub/> 1–0 S(1) narrow-band images of both targets and <i>HK<i/> band spectrum of two main stars in I20293 are presented. The spectral energy distibutions (SED) of the stars enclosed in the H<sub>2<sub/> rings are constructed using photometry from the literature and combining with newly obtained Spitzer-MIPS 70 <i>μ<i/>m photometry. The SEDs are modelled using a grid of radiative transfer models to obtain estimates of the star, disk and envelope physical parameters. <i>Results. <i/>The images reveal ring-like structures surrounding isolated young B-type stars. The modelling attributes a mass and age of ~7 <i>μ<i/>m and ~0.1 Myr, respectively, to both young stars, in agreement with other observational indicators. The HK band spectra of I20293 display the Brackett series of HI recombination lines, which appears to correspond exclusively to the young star inside this IRAS source. The ring around I20293 appears to be a single well-defined ellipse with inner parts shining brightly in the Spitzer broad band images and outer parts displaying strong H<sub>2<sub/> emission. In the source I05358, at least two ring's are found, one circumscribing the other. The emission in the Spitzer bands and the H<sub>2<sub/> emission are mostly coincident for the inner ring. The outer ring is visible partly in the Spitzer bands and partly in H<sub>2<sub/> emission. The rings in both the sources, I20293 and I05358, have diameters of ~25 000–30 000 AU. The envelope sizes estimated by the SED modelling are consistent with the size of the rings estimated using the imaging data. The spectrum of the H<sub>2<sub/> ring in I20293 is suggestive of fluorescent excitation. In the source I05358, the inner ring displays a combination of PAH and H<sub>2<sub/> line emission with excess PAH emission closer to the star.

Detection of unidentified infrared bands in a Hαfilament in the dwarf galaxy NGC 1569 with AKARI

We performed observations of NGC1569 for 6 infrared bands (3.2, 4.1, 7, 11, 15, and 24 micron) with the Infrared Camera (IRC) onboard AKARI. Near- to mid-infrared (2--13 micron) spectroscopy of a Halpha filament was also carried out with the IRC. The extended structure associated with a Halpha filament appears bright at 7 micron, suggesting that the filament is bright at the UIR band emission. Follow-up spectroscopic observations with the IRC confirm the presence of 6.2, 7.7, and 11.3 micron emission in the filament. The filament spectrum exhibits strong 11.3 micron UIR band emission relative to the 7.7 micron band compared to the galaxy disk observed with the Infrared Spectrograph on Spitzer. The near-infrared spectrum also suggests the presence of excess continuum emission in 2.5--5 micron in the filament. The Halpha filament is thought to have been formed by the galactic outflow originating from the star-formation activity in the disk of NGC1569. The destruction timescale of the UIR band carriers in the outflow is estimated to be much shorter (~ 1.3 x 10^3 yr) than the timescale of the outflow (~ 5.3 Myr). Thus it is unlikely that the band carriers survive the outflow environment. Alternatively, we suggest that the band carriers in the filaments may be produced by the fragmentation of large carbonaceous grains in shocks, which produces the Halpha emission. The NIR excess continuum emission cannot be accounted for by free-free emission alone and a hot dust contribution may be needed, although the free-free emission intensity estimated from HI recombination lines has a large uncertainty.

AKARINEAR- AND MID-INFRARED SPECTROSCOPY OF APM 08279+5255 ATz= 3.91

We present rest-frame optical/near-infrared spectra of the gravitationally lense d quasar APM 08279+5255 at $z=3.91$ that has been taken using the Infrared Camera (IRC) onboard the AKARI infrared satellite. The observed continuum consists of two components; a power-law component dominating optical wavelengths which is the direct light from the central source and thermal emission dominating near-infrared wavelengths which is attributed to the emission from hot dust in the circumnuclear region. The thermal emission well represents optically thick emission by hot dust at T ~ 1300K with tau(2micron)> 2 and apparent mass, M(hot) >10 M_sun. Thus, our observations directly detected the optically thick region of hot dust in APM 08279+5255. HI recombination lines of H_alpha(0.656micron), Pa_alpha(1.875micron), and Pa_beta(1.282micron) are clearly detected at 3.2, 6.3, and 9.3 micron. Simulations with the photoionization models suggest that APM 08279+5255 has BLR(Broad Line Region) clouds characterized by log n_{H} ~ 12- 14 for the gas density, log U ~ -2 - -6$ for the ionization parameter, and E(B-V) ~ 0.3-0.6$for the broad line region. Thus, optically thick emission of hot dust support an idea on non-spherical distribution of dust near the central source, consistent with the Active Galactic Nuclei model with the dust torus. The temperature of hot dust and flux ratios of these HI lines are similar to those observed in low-redshift quasars. There are significant time-variations in the HI lines, which are probably caused by variations in the brightness of the central source.

행성상 성운 NGC 6881의 운동학적 특성과 기하학적 구조

행성상성운 NGC 6881은 4극자형태를 이루고 있고 JET이 영상에 나타난다. Lick 천문대에 있는 Hamilton Echelle Spectrograph(HES)을 사용하여 관측한 가시광 영역의 방출선 스펙트럼의 선윤곽을 연구하였다. 우리가 연구하는 HES 분광 자료는 직경이 4초각인 영역의 안쪽에서 관측된 것이다. IRAF와 StarLink/Dipso분석프로그램을 사용하여 HI, HeI, HeII, [OIII], [NII], [ArIII], [SII], [SIII] 등의 강한 선들의 선윤곽을 통해 팽창속도를 얻었다. HI선의 경우 단일 정상을 보이는 반면, He과 다른 금지선들은 두 개의 정상 분포가 겹치는 특성을 보였다. 가스 유출 속도는 중심별의 복사압에 의해 바깥쪽으로 갈수록 가속되는 것으로 분석되었다. 우리는 팽창속도자료를 통해, HST 영상에서 보여진 중심부분의 세 개의 고리는 양극콘(HI 선등에 나타남)과 고리(He, [SIII]선에 특성이 보임)의 복합 구조가 투영된 것으로 결론지었다. The Planetary nebula NGC 6881 displays quadrupole morphology and it also has a jet feature in its image. We investigated the line profiles of the optical region spectral emission lines, using the Hamilton Echelle Spectrograph (HES) at the Lick observatory. The HES data obtained in this study was the radiation coming from the inner region within the diameter of 4 second of arc. Expansion velocity was obtained, based on the strong emission line profiles of e.g. H, Hel, Hell, [OIII], [NII], [ArIII], [SII], and [SIII}, using the IRAF and StarLink/Dipso reduction packages. The HI recombination lines showed one single peak profile, while the He and forbidden strong lines displayed double peaks. The results of this study show that the outflow velocity of gas increases radially outwards due to the central stellar radiation pressure. It was concluded that three central rings appeared in the HST image are the result of a combined structure of bipolar cones (seen in e.g. HI lines) and a ring (seen in He, [SIII] lines) in projection.

ISO Observations of Be Stars

AbstractWe discuss the infrared spectral energy distribution of Be stars, focusing on new results obtained with the Infrared Space Observatory. The 60-160 μm flux of some Be stars is higher than expected, which may be due to cold dust or an outer disk component with enhanced densities. The infrared spectrum of Be stars is dominated by numerous HI recombination lines, whose line strengths show a complex behaviour. The electron temperature in the disk of ϒ Cas was found to be about 9500 K, and evidence for an elevated temperature near the upper part of the disk is presented. Be stars may be recognized from their infrared spectrum on the basis of HI line flux ratios.

A near-infrared spectral survey of Planetary Nebulae

We have completed a near-infrared spectral survey of more than 40 planetary nebulae (PN). The data were obtained using the KSPEC spectrometer on the University of Hawaii 2.2m telescope on Mauna Kea. KSPEC is a cross-dispersed spectrograph that provides simultaneous sampling of the 1.1–2.4 μm range at a resolution of approximately 700. We used a 1 × 7 arcsec slit and a slit-viewing camera with a second NICMOS3 detector operating in the K-band for positioning and tracking of the source. The survey sample consists of compact IR-bright PN with a range of ages and morphological classifications. For many PN in the survey, spectra of several positions, such as the central star and one or more positions in the nebula, were obtained. There are many spectral features of interest within this wavelength range, such as HI recombination lines, emission lines of HeI, FeI, OI, and [FeII]; molecules such as H2, CN, C2, and CO; and continuum emission from the central star and hot dust in the nebula. A typical spectrum is shown in Figure 1. Emission from H2 was detected for the first time in several PN, including NGC 40, NGC 7026, M 1-92, and Vy 2-2. The survey data will be used to compare the properties of the sample PN, including H2 excitation mechanisms (shocks versus excitation by UV photons) and temperatures, and to correlate the properties with morphology class and age.

The relation between cerenkov redshift of H-I lines of quasars and the intensity ratio lyman-alpha / CIV

In the framework of the Cerenkov line enission theory we discuss the intrinsic relation between the Cerenkov redshift of HI emission lines of quasars and the line intensity ratio I(Lyα) I(Hβ) . Neglecting the contributions of HI recombination lines in the outer optically thin zones of quasars we can use the observed relative shift of the Lyα line with respect to the CIV line, i.e., the Cerenkov redshift, to obtain an estimate of the particle population at the 2nd energy level, R 2≈ 0.02. We can also use the observed 〈 I(Hα) I(Hβ) 〉 value to estimate the parameter Xβ ≈ 14.0. For a temperature of ∼11000 K, the predicted Cerenkov redshifts of HI Balmer lines and the intensity ratio I(Lyα) I(Hβ) are then both in good agreement with the observations. This is a strong support for the Cerenkov line emission theory.