Radial Velocities Of Emission Lines Research Articles

Stable accretion in young stars: the cases of EX Lupi and TW Hya

ABSTRACT We examine the long-term spectroscopic and photometric variability of EX Lupi and TW Hya, studying the presence of stable accretion and the role it plays in the observed variability. Analysing the velocity modulations of the emission lines with star-melt, we obtain information on the structure of the accretion columns and the disc–star connection. The emission-line radial velocities reveal that TW Hya, like EX Lupi, has a remarkably stable or slow-varying accretion column footprint, locked to the star for several years. The line-emitting regions are non-polar for both EX Lupi and TW Hya, and species with different energies differ in position. In contrast, the continuum emission as observed in the photometry is very variable and can be modelled by hotspot(s) that change over time in phase, shape, temperature, size, and location with respect to the emission-line region. The continuum emission region may not be limited to the stellar surface, especially during episodes of high accretion. The broad-line emission observed in EX Lupi during episodes of increased accretion reveals a further structure, which can be fitted by non-axisymmetric disc in Keplerian rotation inwards of the corotation radius. Since the radial velocity modulation due to accretion footprints is so stable, we used it to search for further velocity modulations. While no residual modulation (other than caused by stellar rotation) is found in these objects, a similar analysis could help to identify young planets/companions. Therefore, determining whether stable accretion footprints are common among young stars is a key to detect young planets.

Measuring interacting binary mass functions with X-ray fluorescence

ABSTRACT The masses of compact objects in X-ray binaries are best constrained through dynamical measurements, relying on radial velocity curves of the companion star. In anticipation of upcoming high X-ray spectral resolution telescopes, we explore their potential to constrain the mass function of the compact object. Fe K line fluorescence is a common feature in the spectra of luminous X-ray binaries, with a Doppler-broadened component from the inner accretion disc extensively studied. If a corresponding narrow line from the X-ray irradiated companion can be isolated, this provides an opportunity to further constrain the binary system properties. Here, we model binary geometry to determine the companion star’s solid angle, and deduce the iron line’s equivalent width. We find that for systems with a mass ratio q > 0.1, the expected Kα equivalent width is 2–40 eV. Simulations using xspec indicate that new microcalorimeters will have sufficient resolution to be able to produce Kα emission-line radial velocity measurements with precision of 5–40 km s−1, for source continuum fluxes exceeding 10−12 erg cm−2 s−1. Several caveats need to be considered; this method is dependent on successful isolation of the narrow line from the broad component, and the observation of clear changes in velocity independent of scatter arising from complex wind and disc behaviour. These issues remain to be proven with microcalorimeters, but this method has the potential to constrain binary parameters where optical measurements are not viable.

When the disc’s away, the stars will play: dynamical masses in the nova-like variable KR Aur with a pinch of accretion

ABSTRACT We obtained time-resolved optical photometry and spectroscopy of the nova-like variable KR Aurigae in the low state. The spectrum reveals a DAB white dwarf (WD) and a mid-M dwarf companion. Using the companion star’s i-band ellipsoidal modulation we refine the binary orbital period to be P = 3.906519 ± 0.000001 h. The light curve and the spectra show flaring activity due to episodic accretion. One of these events produced brightness oscillations at a period of 27.4 min, that we suggest to be related with the rotation period of a possibly magnetic WD at either 27.4 or 54.8 min. Spectral modelling provided a spectral type of M4–5 for the companion star and $T_{1}=27\, 148$ $\pm \, 496$ K, $\log \, g=8.90 \pm 0.07$, and $\log (\mathrm{He/H})= -0.79^{+0.07}_{-0.08}$ for the WD. By simultaneously fitting absorption- and emission-line radial velocity curves and the ellipsoidal light curve, we determined the stellar masses to be $M_1 = 0.94^{+0.15}_{-0.11}\, {\rm{M}_{\rm \odot}}$ and $M_2 = 0.37^{+0.07}_{-0.07}\,{\rm{M}_{\rm \odot}}$ for the WD and the M-dwarf companion, respectively, and an orbital inclination of $47^{+1^{\rm o}}_{-2^{\rm o}}$. Finally, we analyse time-resolved spectroscopy acquired when the system was at an i-band magnitude of 17.1, about 1.3 mag brighter than it was in the low state. In this intermediate state, the line profiles contain an emission S-wave delayed by ≃0.2 orbital cycle relative to the motion of the WD, similar to what is observed in SW Sextantis stars in the high state.

An Optical Study of Two VY Sculptoris-type Cataclysmic Binary Stars: V704 And and RX J2338+431

Abstract We report observations of the known cataclysmic variable star (CV) V704 And, and also confirm that the optical counterpart of the ROSAT Galactic Plane Survey source RX J2338+431 is a heretofore-neglected CV. Photometric and spectroscopic observations from MDM Observatory show both systems to be nova-like variables that exhibit dips of 4–5 mag from their mean brightnesses, establishing them as members of the VY Scl subclass. From high-state emission-line radial velocities, we determine orbital periods of 0.151424(3) days (3.63 hr) for V704 And and 0.130400 (1) days (3.13 hr) for RX J2338+431. In V704 And, we find that the Hα emission-line measures cluster into distinct regions on a plot of equivalent width versus full width at half-maximum, which evidently correspond to high, intermediate, and low photometric states. This allows us to assign spectra to photometric states when contemporaneous photometry is not available, an apparently novel method that may be useful in studies of other novalikes. Our low-state spectra of RX J2338+431 show features of an M-type secondary star, from which we estimate a distance of 890 ± 200 pc, in good agreement with the Gaia DR2 parallax.

The very massive X-ray bright binary system Wack 2134 (= WR 21a)★

Fil: Niemela, Virpi Sinikka. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

Analysis of the variability of the luminous emission line star MWC 314

Context. We investigated the surroundings of MWC 314 in the framework of the study of hot emission line star environments using the SAC method. This star is either a B[e] supergiant or a luminous blue variable and appears to be extremely luminous and massive. Aims. We determine the structure and physical conditions of the emitting region and study the possible variations. Methods. We measured the absorption and emission line radial velocities and the emission line fluxes on high-resolution spectra obtained with Aurelie at the 1.52 m OHP telescope in July 1998, with Elodie at the 1.93 m OHP telescope at various epochs, and with echelle spectrographs of the Asiago and Loiano observatories (Italy) in 2006. We used the statistical approach of the self-absorption curve method (SAC) to derive physical parameters of the line-emitting region. Results. We detected drastic variations of the photospheric absorption line radial velocities with time, while the emission line velocities appear to be stable. The Cr II, Ti II, and Fe II emission lines have a complex structure. They are double-peaked, and each of these two 60 km s -1 separated components, is composed of a narrow and a broad component, while the [Fe II] line components are narrower. The fit of the various components of the Fe II lines to a SAC curve indicates that their intensities are affected by some self absorption. We obtained a Boltzmann-type population law whose mean excitation temperature is 6500 +1500 -1000 K for the narrow component lower and upper levels. We obtained a higher Boltzmann-type population law of 10 500 +3000 -2000 K for the forbidden transition upper levels. Conclusions. From the absorption lines we confirm the binarity for MWC 314. The periodicity has nevertheless to be improved with a higher sampling frequency. Our results from the emission lines are consistent with line formation in a rotating disk around a star. The typical minimum radius of the line emitting region obtained from the SAC study is 3.5 x 10 13 cm (2.0 x 10 13 cm < R < 6.3 x 10 13 cm). We argue, in the framework of a very simplified geometrical model, that the [Fe II] lines are emitted farther out than the permitted Cr II, Ti II, and Fell lines, in a disk inclined 25 ± 5 degrees to the plane of sky. If the rotation of the disk is Keplerian, the Fell lines are emitted in a zone defined by 4 x 10 12 cm < R < 7 x 10 13 cm, while for a rotation with conservation of angular momentum, they are emitted from 4 x 10 12 cm < R < 2 x 10 13 cm.

INFRARED SPECTROSCOPY OF SYMBIOTIC STARS. VI. COMBINED ORBITS FOR TWO S-TYPE SYSTEMS: V455 SCORPII AND SS 73-90

We have combined new infrared radial velocities and previously obtained spectropolarimetric observations to compute orbits of the M6 giants in two southern S-type symbiotic systems. The spectropolarimetric data enable the orbital inclinations of the systems to be determined, placing greater constraints on the properties of the components. V455 Sco has a circular orbit with a period of 1398 ± 6 days and an inclination of 94 ◦ ± 1 ◦ . The orbit of SS 73-90 has a period of 898 ± 5 days, a modest eccentricity of 0.16, and an inclination of 97 ◦ ± 7 ◦ . The center of mass velocity of each system is large, −77.9 km s −1 for V455 Sco and 89.5 km s −1 for SS 73-90, making them members of the old disk population. The M giant component of each system is likely on the asymptotic giant branch. From estimates of the M giants’ radii we predict that both systems are eclipsing and provide ephemerides to search for the eclipses. For V455 Sco, the predicted eclipses are found in data from the Harvard College Observatory plate archives. The Heii emission feature near 1.0123 µm is associated with the hot component in both systems. However, the orbits produced from the emission-line radial velocities do not lead to masses that are consistent with other results.

Robust Models for Phase Shifts in Accreting Binary Stars

Radial velocity studies of accreting binary stars commonly use accretion disk emission lines to determine the radial velocity of the primary star and therefore the mass ratio. These emission line radial velocity curves are often shifted in phase from the expected motion of the primary. These phase shifts cast doubt on the use of disk emission lines in the determination of mass ratios. We present a systematic study of phase shifts, using data from the literature to distinguish between possible explanations of the phase shift. We find that one widely adopted class of models is contradicted by observations (section 2). We present a generalized form of another class of models, which we call offset models. We show that these models are quantitatively consistent with existing data (figures 2 and 3, and the discussion in section 4.4). We consider the implications of adopting measurement offset models, for both disk structure and determination of binary parameters. Specifically, we describe in section 6 how measurement offset models may be used improve determinations of the mass ratio based on disk emission lines. This could be a valuable new tool in determining masses of important astrophysical objects such as accreting neutron stars and black holes.

Hubble Space TelescopeSpace Telescope Imaging Spectrograph Spectroscopy of the Intermediate Polar EX Hydrae

We present the results of our analysis of six orbits of Hubble Space Telescope Space Telescope Imaging Spectrograph (HST/STIS) time-tagged spectroscopy of the intermediate polar, EX Hydrae. The high time and wavelength resolution of the HST/STIS spectra provided an excellent opportunity to study the UV properties of EX Hya. Measurements of the continuum and emission-line fluxes corroborate earlier studies that show that the emission-line fluxes are modulated more strongly than the continuum flux and originate from the accretion curtains, while the continuum flux originates from the white dwarf photosphere. The measured K amplitude of the narrow emission-line radial velocity curve is used to calculate a white dwarf mass of 0.91 ± 0.05 M☉. Synthetic white dwarf photosphere and accretion disk spectral models are used to further refine the white dwarf and accretion disk properties. Using the spectral models, it is determined that EX Hya has a white dwarf of mass 0.9 M☉, T = 23,000 K, and an accretion disk truncated at 2.5RWD and is at a distance of 60 pc.

The white dwarf revealed in the intermediate polar V709 Cassiopeiae

Results are presented from the first detailed spectroscopic observations of the recently identified intermediate polar RXJ0028.8+5917/V709 Cas. The study of the emission line radial velocities allows us to remove the uncertainties on the different aliases of the orbital period and a best value is found at (0.2225 +/- 0.0002) day. It is also found that the system shows significant EW~ (2-4)A, broad absorptions affecting the Balmer lines from Hdelta to Hbeta. These broad absorptions are interpreted as the contribution of an underlying white dwarf atmosphere. The characteristics of the absorptions are found to be consistent with a DA log(g) = 8 white dwarf at a temperature of ~ 23 000 K, contributing ~ 17 % (at 4500 A) to the overall flux. This is the first direct detection of a white dwarf in an intermediate polar system. The absence of significant Zeeman splitting indicates a magnetic field lower than 10 MG, confirming that, at least in some cases, intermediate polars have weaker fields than polars. Different possibilities are discussed to explain the substantial contribution of the white dwarf to the overall flux.

Orbital Period of the Low‐Inclination SW Sextantis Star V442 Ophiuchi

V442 Ophiuchi is a low-inclination (noneclipsing) nova-like cataclysmic variable. We have obtained medium resolution (1-3.5 A), time-resolved optical spectroscopy of this interacting binary star spanning an interval of 4 yr, from 1995 August to 1999 June. Using an Hα radial velocity curve constructed from our combined spectroscopic data sets, we have determined that Porb = 0.1243 days for V442 Oph, breaking the long-standing 1 day alias ambiguity in its orbital period. V442 Oph shares many of the characteristics of the group of cataclysmic variables known as the SW Sextantis stars. Its Doppler tomograms and orbital phase-dependent emission-line behavior, including the occurrence of a prominent transient absorption event, are consistent with those of other SW Sex stars. V442 Oph also displays single-peaked rather than double-peaked emission lines, strong He II λ4686 emission, and a phase offset of +0.08 between the Hα emission-line radial velocities and the phasing of He II. We discuss the role of V442 Oph as one of three known low-inclination examples of SW Sex stars. Like the other low-inclination SW Sex stars, LS Pegasi and V795 Herculis, the Balmer emission lines in V442 Oph have high velocity components that extend to ≈±1900 km s-1 and follow an apparent S-wave pattern in the trailed spectrum. Finally, we compare two models for the SW Sex stars involving accretion stream overflow, in the context of a low-inclination system in which our line of sight likely extends over the entire face of the disk.

The End of the Lines for OX 169: No Binary Broad‐Line Region

We show that unusual Balmer emission line profiles of the quasar OX 169, frequently described as either self-absorbed or double peaked, are actually neither. The effect is an illusion resulting from two coincidences. First, the forbidden lines are quite strong and broad. Consequently, the [N II]6583 line and the associated narrow-line component of H-alpha present the appearance of twin H-alpha peaks. Second, the redshift of 0.2110 brings H-beta into coincidence with Na I D at zero redshift, and ISM absorption in Na I D divides the H-beta emission line. In spectra obtained over the past decade, we see no substantial change in the character of the line profiles, and no indication of intrinsic double-peaked structure. The H-gamma, Mg II, and Ly-alpha emission lines are single peaked, and all of the emission-line redshifts are consistent once they are correctly attributed to their permitted and forbidden-line identifications. A systematic shift of up to 700 km/s between broad and narrow lines is seen, but such differences are common, and could be due to gravitational and transverse redshift in a low-inclination disk. Stockton & Farnham (1991) had called attention to an apparent tidal tail in the host galaxy of OX 169, and speculated that a recent merger had supplied the nucleus with a coalescing pair of black holes which was now revealing its existence in the form of two physically distinct broad-line regions. Although there is no longer any evidence for two broad emission-line regions in OX 169, binary black holes should form frequently in galaxy mergers, and it is still worthwhile to monitor the radial velocities of emission lines which could supply evidence of their existence in certain objects.

BR Lupi: Evidence for a High‐Inclination SU Ursae Majoris Starwith Orbital Period 1.91 Hours

ABSTRACTWe have found cyclic light variations with high amplitude during quiescence possibly reflecting the binary motion of the cataclysmic variable BR Lupi. With this hypothesis, an orbital frequency of 12.573 (1.91 hr) ± 0.071 cycles day−1 is derived. In addition, differential photometry obtained during the 1995 March superoutburst shows superhumps with amplitude 0.25 mag and frequency 12.171 (1.97 hr ) ± 0.106 cycles day−1. Hα emission line radial velocities measured during the decline of the superoutburst follow the orbital motion with half‐amplitude 54 ± 16 km s−1. The mass function along with several empirical and theoretical constraints enabled us to estimate the primary mass M1 = 1.0(1) M⊙, the secondary mass M2 = 0.146(1) M⊙, and the inclination angle (50°<i<65°).

The new intermediate polar RX J1238 – 38: a system below the period gap?

We present optical observations of the recently discovered ROSAT source RX J1238 ‒ 38, which is a new member of the intermediate polar class of asynchronous magnetic cataclysmic variables (CVs). Optical photometry reveals two coherent periodicities at 1860 and 2147 s respectively, with similar amplitudes of ∼8 per cent. Infrared (J-band) intensity variations are detected only at the 1860-s period, at an amplitude of ∼15 per cent. The initial hypothesis, that these two periods were the spin and synodic (i.e., beat) period respectively, appears not to be supported by the spectroscopic data. The emission lines vary on the longer photometric period, and radial velocity variations are detected at this period and at a longer period of ∼5300 s, which we identify as the spin and orbital periods respectively. The most likely explanation for the 1860-s period is that it is the first harmonic of the ω − Ω sideband, leading to an improved determination of the orbital period as 5077 s (= 84 min). If this interpretation is correct, RX J1238 − 38 joins EX Hya as the only other intermediate polar below the 2‒3 h period gap, and with an orbital period close to the minimum for CVs with non-degenerate secondaries. The spin-modulated emission-line radial velocities and widths appear to be anticorrelated, with maximum width occurring at maximum blueshift. Such an anticorrelation is expected for aspect changes of accretion curtains. Polarimetric observations of RX J1238 − 38 were inconclusive, although we can put a limit of 0.4 per cent on any variability on the circular polarization, and certainly there is no indication of variations at the photometric or spectroscopic periods.

HS 0551+7241: A New Possible Magnetic Cataclysmic Variable in the Hamburg-C[CLC]f[/CLC]A Bright Quasar Survey

We present an analysis of spectroscopic observations of a newly discovered cataclysmic variable, HS 0551+7241. In 1995, the star's brightness dropped by ΔB ~ 2.5 mag and HS 0551+7241 entered a low state lasting for ~2 yr. The Hα, Hβ, and He II λ4686 emission-line radial velocity curves show evidence of short ~50 minute fluctuations superposed on longer, ~4 hr, variations. We find similar modulations in the line fluxes and the line equivalent widths. The continuum magnitude light curves suggest that HS 0551+7241 may be an eclipsing system. If the 4 hour period is related to the orbital period, then the mass function is ~0.138 M⊙. Relatively strong He II λ4686 emission and short fluctuations may suggest that the binary is an intermediate polar. In that case, the ~50 minute variations would correspond to an Alfven radius of ~3 × 1010 cm.

Measuring the Motion of the Black Hole in GRO J1655−40

We report optical spectroscopic observations of the low-mass X-ray binary GRO J1655-40 during outbursts in 1994 August-September and in 1996 June. The spectra show emission and absorption lines from the accretion disk surrounding the X-ray source, which have enabled us to measure the motion of the black hole candidate in this system. It is the first time among black hole candidates that an emission-line radial velocity curve is seen in phase with the expected motion of the primary. The projected radial velocity semiamplitude determined for the primary (KX = 76.2±7.5 km s-1), combined with estimates of the projected radial velocity semiamplitude of the companion star from previous observations (KC=228.2±3.0 km s-2), yields a 95% confidence limit, derived purely from kinematics, of MX > 5.1 M☉ for the mass of the compact object in GRO J1655-40, confirming its black hole nature.

Observations of the SW Sextantis Star BH Lyncis in a High State

We present time-resolved photometry and medium resolution (2 A) spectroscopy of the SW Sextantis star BH Lyncis obtained during a high state of the system. Previous detailed observations have been obtained only during low and intermediate states. In addition, we present the first International Ultraviolet Explorer low-resolution (6 A) spectrum of BH Lyn. A revised photometric ephemeris, HJD(min) = 2,447,180.3366(2) + 0.15587535(6)E, is derived based on new and previously published eclipse timings. The amplitude of the pre-eclipse hump in light curves of BH Lyn is shown to vary, suggesting that the degree to which the incoming accretion stream impacts the edge of the disk changes over time. We estimate system parameters using the V-band eclipse width and He II λ4686 emission-line radial velocity (i ≈ 79°, q ≈ 0.45, MWD ≈ 0.7 M☉, M2 ≈ 0.3 M☉, R2 ≈ 0.4 R☉, a ≈ 1.2 R☉). Doppler tomograms constructed for the prominent emission lines in BH Lyn show a lack of emission at the expected locations of the bright spot and accretion stream trajectories. The differences between the low and high states of BH Lyn are discussed, along with the possible origin of a significant amount of the emission-line flux in a wind from the disk and/or white dwarf primary star. Finally, a model involving the presence of vertically extended bulges in the accretion disk is introduced to explain the characteristic phase-dependent absorption feature found in emission lines of the SW Sex stars.

ORBITAL PERIODS FOR THE UNUSUAL DWARF NOVAE ER URSAE MAJORIS AND V1159 ORIONIS

ABSTRACT ER UMa (PG 0943+521), V1159 Ori, and RZ LMi constitute a small recently- recognized group of dwarf novae, called the RZ LMi stars or the ER UMa stars. They share many features of the SU UMa-type, but have shorter outburst cycles than had been known previously. Here we establish orbital periods, based on emission-line radial velocities, for ER UMa (0.06366 ± 0.00003 d = 91.67 ± 0.04 min) and V1159 Ori (0.06217801 ± 1.3 × 10-7 d = 89.5363 ± 0.0002 min). The precise orbital period for V1159 Ori depends on an extrapolation of cycle count from 1991 to 1994, which is slightly uncertain, but the daily cycle count is reasonably secure. These orbital periods are similar to those of the more common, less frequently outbursting SU UMa stars. As is generally the case, the orbital periods derived here are slightly shorter than the periods of photometric superhumps which appear in superoutburst. The superhump period excesses found here are compatible with, but marginally larger than, those seen in other SU UMa stars of similar period. While the empirical link between ER UMa stars and SU UMa stars is generally strengthened by these results, the trend toward slightly larger period excesses (if true) can be interepreted as a tendency for systems with larger mass ratios to develop larger mass-transfer rates at a given orbital period.

Simulating the emission line radial velocity modulation in discless intermediate polars

A code has been developed which simulates the emission line radial velocity modulation expected in a discless intermediate polar, where the bulk of the accretion flow flips from one magnetic pole to the other twice every beat cycle. The situation is found to produce a radial velocity curve which exhibits a modulation at the beat period, although this is not strictly periodic in that it is modified by an intrinsic underlying orbital modulation; i.e., the morphology of the beat modulation over one beat cycle depends on the orbital phase. Interestingly, it is found that, when the resultant velocity curve over one orbital cycle is folded on the beat period and binned coarsely, a quasisinusoidal velocity profile can be reproduced, depending on the values chosen for the various free parameters. An important implication of this result is that the spin period of BG Canis Minoris could indeed be 847 s, and is not necessarily 913 s as we had previously concluded. The model is also capable of reproducing the modulation seen in the newly discovered system RXJ1712.6–2414.

The four periodicities of the cataclysmic variable TV Columbae

I present six nights of simultaneous optical photometry and spectroscopy aimed at observing the four periodicities of TV Col. The 32-min white dwarf spin period (known from the X-ray band) is not convincingly detected in the optical. The 5.5-h orbital period is manifest both photometrically and in the emission-line radial velocities. The emission lines show disc emission with a superimposed S-wave. Near orbital phase 0.8, the S-wave is at inferior conjunction, the photometric variation is at minimum, there is absorption in the line centres and we see X-ray dips. All these findings suggest that the rim of the disc is thickened at this location. The 4-d and 5.2-h cycles dominate the continuum variations but do not change the emission-line profiles. These modulations are not absolutely coherent