Brackett Series Research Articles

The black hole and central stellar population of MCG–6-30-15★

We present the first near-infrared integral field spectroscopy observations of the galaxy MCG--6-30-15. The H-band data studied in this paper cover the central 500 pc of the galaxy at the best resolution (0".1) so far. The spectra of the innermost regions are dominated by broad brackett series emission lines and non-stellar continuum, under which we are able to trace the distribution and kinematics of the stars and also the [Fe II] line emission. We find that there is a counter-rotating stellar core extending out to 125 pc, which appears to be associated with the [Fe II] emission. Based on the mass-to-light ratio, and the presence of this emission line, we estimate the age of the central stellar population to be of order of 65 Myr. We show that the gas needed to fuel the black hole is, at most, only 1 per cent of that needed to form these stars. We derive independent constraints on the black hole mass using the dynamical information and determine an upper limit for the black hole mass, Mbh < 6e7 Msun, that is consistent with other estimates.

Tracers of discs and winds around intermediate- and high-mass young stellar objects

We present a study of the kinematical properties of a small sample of nearby near-infrared bright massive and intermediate mass young stellar objects using emission lines sensitive to discs and winds. We show for the first time that the broad ($\sim500$kms$^{-1}$) symmetric line wings on the HI Brackett series lines are due to Stark broadening or electron scattering, rather than pure Doppler broadening due to high speed motion. The results are consistent with the presence of a very dense circumstellar environment. In addition, many of these lines show evidence for weak line self-absorption, suggestive of a wind or disc-wind origin for that part of the absorbing material. The weakness of the self-absorption suggests a large opening angle for such an outflow. We also study the fluorescent 1.688$\mu$m FeII line, which is sensitive to dense material. We fitted a Keplerian disc model to this line, and find reasonable fits in all bar one case, in agreement with previous finding for classical Be stars that fluorescent iron transitions are reasonable disc tracers. Overall the picture is one in which these stars still have accretion discs, with a very dense inner circumstellar environment which may be tracing either the inner regions of a disc, or of a stellar wind, and in which ionised outflow is also present. The similarity with lower mass stars is striking, suggesting that at least in this mass range they form in a similar fashion.

Near-infrared observations of the Be/X-ray binary pulsar A0535+262

We present the results obtained from extensive near-infrared (IR) spectroscopic and photometric observations of the Be/X-ray binary A0535+262/HDE 245770 at different phases of its ∼111 d orbital period. This observation campaign is part of the monitoring program of selective Be/X-ray binary systems aimed at understanding X-ray and near-IR properties at different orbital phases, especially during the periastron passage of the neutron star. The near-IR observations presented here were carried out using the 1.2 m telescope at the Mt. Abu IR Observatory. Though the source was relatively faint for spectroscopic observations with the 1.2 m telescope, we monitored the source closely during the 2011 February—March giant X-ray outburst to primarily investigate whether any drastic changes in the near-IR J H K spectra took place at the periastron passage. Changes of such a striking nature were expected to be detectable in our spectra. Photometric observations of the Be star show a gradual and systematic fading in the J H K light curves since the onset of the X-ray outburst, which could suggest a mild evacuation/truncation of the circumstellar disk of the Be companion. Near-IR spectroscopy of the object shows that the J H K spectra are dominated by the emission lines of hydrogen Brackett and Paschen series and HeI lines at 1.0830, 1.7002 and 2.0585 μm. The presence of all the hydrogen emission lines in the J H K spectra, along with the absence of any significant change in the continuum of the Be companion during X-ray quiescent and X-ray outburst phases, suggests that the near-IR line emitting regions of the disk are not significantly affected during the X-ray outburst.

NEAR-INFRARED SPECTROSCOPY OF EX Lupi IN OUTBURST

EX Lup is the prototype of the EXor class of young eruptive stars: objects showing repetitive brightenings due to increased accretion from the circumstellar disk to the star. In this paper, we report on medium-resolution near-infrared spectroscopy of EX\,Lup taken during its extreme outburst in 2008, as well as numerical modeling with the aim of determining the physical conditions around the star. We detect emission lines from atomic hydrogen, helium, and metals, as well as first overtone bandhead emission from carbon monoxide. Our results indicate that the emission lines are originating from gas located in a dust-free region within ~ 0.2 AU of the star. The profile of the CO bandhead indicates that the CO gas has a temperature of 2500 K, and is located in the inner edge of the disk or in the outer parts of funnel flows. The atomic metals are probably co-located with the CO. Some metallic lines are fluorescently excited, suggesting direct exposure to ultraviolet photons. The Brackett series indicates emission from hot (10000 K) and optically thin gas. The hydrogen lines display a strong spectro-astrometric signal, suggesting that the hydrogen emission is probably not coming from an equatorial boundary layer; a funnel flow or disk wind origin is more likely. This picture is broadly consistent with the standard magnetospheric accretion model usually assumed for normally accreting T Tauri stars. Our results also set constraints on the eruption mechanism, supporting a model where material piles up around the corotation radius and episodically falls onto the star.

Nova V5579 Sgr 2008: near-infrared studies during maximum and the early decline phase

We present near-infrared spectroscopic and photometric observations of the nova V5579 Sgr during the maximum and early decline phase. The spectra follow the evolution of the nova from peak brightness when the lines had strong P Cygni profiles to a phase dominated by prominent emission lines. The spectra during the emission phase are dominated by strong H I lines from the Brackett and Paschen series, O I and C I lines. The spectra in the final stages of our observations show a rising continuum towards longer wavelengths, indicating dust formation. Dust formation in V5579 Sgr is consistent with the presence of lines of elements with low-ionization potentials like Na and Mg in the early spectra. The early presence of such lines had been earlier suggested by us to be potential indicators of dust formation later in the nova's development. We also discuss the possibility of using P Cygni profiles to probe the properties of the erupting white dwarf during the early outburst.

Using X‐shooter to measure the extinction in long GRB host galaxies from emission lines

AbstractThe spectra of the host galaxies of gamma‐ray bursts at low redshift generally show strong hydrogen lines of the Balmer, Paschen and Brackett series, in addition to strong nebular metal lines. In special cases the hosts can be resolved in separate star forming regions, and spatially resolved spectroscopy can be obtained. Generally, the three strongest Balmer lines are used to derive the reddening experienced by the emission lines of the host gas, assuming a Milky Way extinction curve, case B recombination and a fixed electron temperature. We demonstrate how the wide wavelength range of X‐shooter, in combination with a rigorous calibration strategy, can be used to fit explicitly for RV, Te, and AV simultaneously using a large number of H and He I recombination lines, explicitly corrected for stellar atmosphere absorption. This increases our understanding of extinction and absorption in starforming regions in GRB hosts. We use two GRB hosts as examples of the methods, outlining the advantages of using X‐shooter over other instruments (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

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.

Near-infrared observations of nova V574 Puppis (2004)

We present results obtained from extensive near-infrared spectroscopic and photometric observations of nova V574 Pup during its 2004 outburst. The observations were obtained over four months, starting from 2004 November 25 (four days after the nova outburst) to 2005 March 20. The near-IR JHK light curve is presented - no evidence is seen from it for dust formation to have occurred during our observations. In the early decline phase, the JHK spectra of the nova are dominated by emission lines of hydrogen Brackett and Paschen series, OI, CI and HeI. We also detect the fairly uncommon Fe II line at 1.6872 micron in the early part of our observations. The strengths of the HeI lines at 1.0830 micron and 2.0585 micron are found to become very strong towards the end of the observations indicating a progression towards higher excitation conditions in the nova ejecta. The width of the emission lines do not show any significant change during the course of our observations. The slope of the continuum spectrum was found to have a lambda^{-2.75} dependence in the early stages which gradually becomes flatter with time and changes to a free-free spectral dependence towards the later stages. Recombination analysis of the HI lines shows deviations from Case B conditions during the initial stages. However, towards the end of our observations, the line strengths are well simulated with case B model values with electron density n_e = 10^{9-10} cm^{-3} and a temperature equal to 10^4 K. Based on our distance estimate to the nova of 5.5 kpc and the observed free-free continuum emission in the later part of the observations, we estimate the ionized mass of the ejecta to be between 10^{-5} and 10^{-6} solar-mass.

Hydrogen Stark Broadened Brackett lines

Stark-broadened lines of the hydrogen Brackett series are computed for the conditions of stellar atmospheres and circumstellar envelopes. The computation is performed within the Model Microfield Method, which includes the ion dynamic effects and makes the bridge between the impact limit at low density and the static limit at high density and in the line wings. The computation gives the area normalized line shape, from the line core up to the static line wings.

Infrared Spectra of Young Stars Embedded in the R Coronae Australis Cloud

ABSTRACTInfrared spectra are presented for a magnitude-limited (K < 12.5 mag) sample of stellar objects observed toward the R Coronae Australis molecular core. These spectra, which are used to identify young stellar objects in the cloud, include the wavelengths of emission lines from [Fe II] and H 2, four of the Brackett series lines, the CO bandheads, as well as photospheric absorption lines of Al, Na, Mg, Si, and Ca. For a subset of the sample, the spectra are compared to those of infrared spectral standard stars to derive spectral types and luminosity classes. By comparing their placement in a Hertzsprung-Russell diagram with theoretical pre–main-sequence tracks and isochrones, we estimate the stellar masses and assess the evolutionary states of the members of this young aggregate. All of the sources classified via near-IR spectroscopy have masses in the range 0.2–2.5 M ⊙. The locus of points in the H-R diagram is lower than observed for other embedded clusters (e.g., NGC 2024 and the ρ Oph core), suggesting either a more advanced evolutionary state or a difference in the intrinsic stellar birthline for very young clusters. We discuss the implications of our results for the shape of the initial mass function of the embedded young cluster and the star-forming history of the cloud.

NEAR-INFRARED SPECTROSCOPIC MONITORING OF EXOR VARIABLES: FIRST RESULTS

We present low-resolution spectroscopy in the near-IR (0.8–2.5 μm) of the EXor variables. These are the initial results (obtained during the period 2007–2008) from a long-term photometric and spectroscopic program aimed to study the variability in the accretion processes of pre-main-sequence stars, by correlating the continuum fluctuations with the spectroscopic properties. Eight sources have been observed in different epochs, for a total of 25 acquired spectra. EXor spectra show a wide variety of emission features dominated by H i recombination (Paschen and Brackett series). We have investigated whether line and continuum variability could be due to a variable extinction, but such a hypothesis is applicable only to the peculiar source PV Cep. By comparing the observed spectra with a wind model, mass loss rates in the range (2–10) × 10−8M☉ yr−1 are derived, along with other wind parameters. Consistent results are also obtained by assuming that H i lines are due to accretion. A CO overtone is also detected in the majority of the sources both in absorption and in emission. It appears to come from regions more compact than winds, likely the stellar photosphere (when in absorption) and the circumstellar disk (when in emission). Na i and Ca i IR lines behave as the CO does, thus they are thought to arise in the same locations. For some targets multiple spectra correspond to different activity stages of the source. Those exhibiting the largest continuum variation at 2 μm (ΔK ≳ 1 mag) present a significant line flux fading during the continuum declining phases. In particular, CO absorption (emission) appears associated with inactive (active) stages, respectively.

Radiation line spectra and orbit radii of the hydrogen atom

The orbit radii of the hydrogen atom were calculated using the values of the van der Waals and two covalent radii and the well-known quadratic dependence of the orbit radii on a series of whole numbers (Bohr equation). Using the equation for the orbital velocity of the dynamics of orbital motion, the orbital velocities and emission frequencies for 19 hydrogen atom orbits were determined with the calculated values of the radii. It was shown that for orbits characterized by whole numbers n, equal to 4, 7, 10, 13, 16, and 19, the calculated frequencies coincide with the experimental (handbook) values of the Layman, Balmer, Paschen, Brackett, Pfund, and Humphrey series frequencies. A graph displaying the frequencies of all series, including x-ray, was plotted with the calculated values of the radii and the experimental frequency values. An equation for calculating the radiation frequencies as a function of the orbit radius of the hydrogen atom was proposed and substantiated.

Physical Conditions of Accreting Gas in T Tauri Star Systems

We present results from a low resolution (R~300) near-infrared spectroscopic variability survey of actively accreting T Tauri stars (TTS) in the Taurus-Auriga star forming region. Paschen and Brackett series H I recombination lines were detected in 73 spectra of 15 classical T Tauri systems. The values of the Pan/PaB, Brn/BrG, and BrG/Pan H I line ratios for all observations exhibit a scatter of < 20% about the weighted mean, not only from source to source, but also for epoch-to-epoch variations in the same source. A representative or `global' value was determined for each ratio in both the Paschen and Brackett series as well as the BrG/Pan line ratios. A comparison of observed line ratio values was made to those predicted by the temperature and electron density dependent models of Case B hydrogen recombination line theory. The measured line ratios are statistically well-fit by a tightly constrained range of temperatures (T < 2000 K) and electron densities 1e9 < n_e < 1e10 cm^-3. A comparison of the observed line ratio values to the values predicted by the optically thick and thin local thermodynamic equilibrium cases rules out these conditions for the emitting H I gas. Therefore, the emission is consistent with having an origin in a non-LTE recombining gas. While the range of electron densities is consistent with the gas densities predicted by existing magnetospheric accretion models, the temperature range constrained by the Case B comparison is considerably lower than that expected for accreting gas. The cooler gas temperatures will require a non-thermal excitation process (e.g., coronal/accretion-related X-rays and UV photons) to power the observed line emission.

Measuring the physical conditions of accreting gas in T Tauri systems

AbstractHydrogen emission lines observed from T Tauri stars (TTS) are associated with the accretion/outflow of gas in these young star forming systems. Magnetospheric accretion models have been moderately successful at reproducing the shapes of several Hi emission line profiles, suggesting that the emission arises in the accretion funnels. Despite considerable effort to model and observe these emission features, the physical conditions of the gas confined to the funnel flows remain poorly constrained by observation. We conducted a mutli-epoch near-infrared spectroscopic survey of 16 actively accreting classical TTS in the Taurus-Auriga star forming region. We present an analysis of these simultaneously acquired line flux ratios of many Paschen and Brackett series emission lines, in which we compare the observed ratios to those predicted by the Case B approximation of hydrogen recombination line theory. We find that the line flux ratios for the Paschen and Brackett decrements as well as a comparison between Brγ and Paschen transitions agree well with the Case B models with T &lt; 5000 K and ne ≈ 1010 cm−3.

Toward Mapping the Detailed Density Structure of Classical Be Circumstellar Disks

The first results from a near-contemporaneous optical and infrared spectroscopic observing program designed to probe the detailed density structure of classical Be circumstellar disks are presented. We report the discovery of asymmetrical infrared emission lines of He I, O I, Fe II, and the Brackett, Paschen, and Pfund series lines of H I which exhibit an opposite V/R orientation (V $>$ R) to that observed for the optical Balmer H$\alpha$ line (V $<$ R) in the classical Be star $\zeta$ Tau. We interpret these data as evidence that the density wave which characterizes $\zeta$ Tau's disk has a significantly different average azimuthal morphology in the inner disk region as compared to the outer disk region. A follow-up multi-wavelength observational campaign to trace the temporal evolution of these line profile morphologies, along with detailed theoretical modeling, is suggested to test this hypothesis.

Evidence for T Tauri-like emission in the EXor V1118 Ori from near-IR and X-ray data

Aims. We present a near-IR study of the EXor variable V1118 Ori, performed by following a slightly declining phase after a recent outburst. In particular, the near-IR (0.8-2.3 µm) spectrum, obtained for the first time, shows a wide variety of emission features of the H i (Paschen and Brackett series), He i recombination, and CO overtone. Methods. By comparing the observed spectrum with a wind model, a mass loss rate of 4 × 10 −8 Myr −1 can be derived along with other parameters whose values are typical of an accreting T Tauri star. In addition, we have used X-ray data from the XMM archive, taken in two different epochs during the declining phase monitored in IR. The X-ray emission (in the range 0.5-10 keV) permits us to derive several parameters (as plasma temperatures and LX luminosity) that confirm the T Tauri nature of the source. Results. In the near-IR, the object maintains a low extinction (AV < 2) during all the activity phases, confirming that variable extinction does not contribute to brightness variations. The lack of both a significant amount of circumstellar material and any evidence of IR cooling from collimated jet/outflow driven by the source indicates that at least this member of the EXor class is in a late stage of the pre-main sequence evolution. When going from inactive to active phases, the luminosity increases considerably (from 1.4 L� to more than 25 L� ) and the observed spectral energy distribution assumes different shapes, all typical of a T Tauri star. In the X-ray regime, an evident fading is present, detected in the post-outburst phase, which cannot be reconciled with the presence of any absorbing material. This circumstance, combined with the persistence (in the pre- and post-outburst phases) of a temperature component at about 10 MK, suggests that accretion has some influence in regulating the coronal activity.

Near-infrared and optical studies of the fast nova V4643 Sgr (Nova Sagittarii 2001)

V4643 Sagittarii or Nova Sagittarii 2001 was discovered in outburst at 7.7 mag. on 2001 February 24. Here, we present near-infrared results of this fast classical nova obtained in the early decline phase in 2001 March followed by optical observations about one month later. Subsequently we also present near-infrared spectra taken later in the nova's evolution, about four months after the outburst, when V4643 Sgr had entered the coronal phase. The spectra in the early decline phase are dominated by emission lines of the HI Brackett series and also the Paschen beta and gamma lines. We study the cause of the excitation of the the OI line at 1.128 micron and discuss the variation in its strength with time after outburst. We discuss the role of optical depth effects on the observed strengths of the hydrogen Brackett and Paschen lines and discuss possible reasons for the puzzling behavior of the Br gamma line strength and whether it is correlated with the OI 1.128 micron line behavior. An optical spectrum is presented which shows that HeII lines are the most prominent features - after HI - to be seen in early 2001 April. We present and also discuss spectra taken in 2001 June and August which prominently show coronal lines of [Si VI] and [Si VII] at 1.9641 micron and 2.4807 micron respectively.

Near infrared studies of the massive X-ray binary 2S 0114+65

We present near-infrared spectroscopy of the massive X-ray binary 2S 0114+650. These observations covering the spectral range 1.08–2.35 μm span the region where Paschen and Brackett series recombination lines of hydrogen are expected to be seen, namely, Paβ , Brγ and Br 10–17 lines. The absence of any of these lines in emission supports earlier inferences that the optical component in 2S 0114+650 is unlikely to be a Be star but rather a B type supergiant. Near-IR photometry gives J = 8.78, H = 8.53 and K = 7.96; these values show marginal variations from earlier reported measurements.

WR 143: a Wolf-Rayet binary

Near infrared spectroscopy and photometry of the Wolf-Rayet Star WR 143 (HD 195177) were obtained in the $JHK$ photometric bands. High resolution spectra observed in the J and H bands exhibit narrow 1.083-micron He I line and the H I Pa Beta and the Brackett series lines in emission superposed on the broad emission line spectrum of the Wolf-Rayet star, giving strong indications of the presence of a companion. From the narrow emission lines observed, the companion is identified to be an early-type Be star. The photometric magnitudes exhibit variations in the JHK bands which are probably due to the variability of the companion star. The flux density distribution is too steep for a Wolf-Rayet atmosphere. This is identified to be mainly due to the increasing contribution from the early-type companion star towards shorter wavelengths.

The imprint of cosmological hydrogen recombination lines on the power spectrum of the CMB

We explore the imprint of the cosmological hydrogen recombination lines on the power spectrum of the cosmic microwave background (CMB). In particular, we focus our analysis in the three strongest lines for the Balmer, Paschen and Brackett series of hydrogen. We expect changes in the angular power spectrum due to these lines on the level of $0.3 \mu K$ for the H$\alpha$ line, being maximum at small angular scales ($\ell \approx 870$). The morphology of the signal is very rich. It leads to relatively narrow spectral features ($\Delta \nu / \nu \sim 10^{-1}$), with several regions in the power spectrum showing a characteristic change of sign of the effect as we probe different redshifts or different multipoles by measuring the power spectrum at different frequencies. It also has a very peculiar dependence on the multipole scale, connected with the details of the transfer function at the epoch of scattering. In order to compute the optical depths for these transitions, we have evolved numerically the populations of the levels of the hydrogen atom during recombination, treating simultaneously the evolution of helium. For the hydrogen atom, we follow each angular momentum state separately, up to the level n=10. Foregrounds and other frequency dependent contaminants, as Rayleigh scattering, may be a important limitation for these measurements, although the peculiar frequency and angular dependences of the effect which we are discussing might permit to separate it. Detection of this signal using future narrow-band spectral observations can give information about the details of how the cosmic recombination proceeds, and how Silk damping operates during recombination.