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Iron line cooling of Be star circumstellar discs
We investigate the effect of line cooling due to iron on the predictedtemperature distributions in Be star circumstellar envelopes. Thisanalysis is applied to the early-type Be star, γ Cas, and thelate-type Be star, 1 Del, to assess the effect of line cooling due tometals in the circumstellar material over a range of spectral type. Wefind that iron, and by analogy other abundant metals, can play a role inthe energetics of Be star discs by providing both heating fromphotoionization and cooling by the escape of collisionally excitedspectral line radiation. The efficiency of the heating and cooling dueto iron varies throughout the circumstellar disc and depends on localphysical conditions. Overall, including iron at the solar abundance doesnot significantly change the volume or density-weighted averagetemperatures in either γ Cas or 1 Del from that predicted by apure hydrogen envelope. However, with an increased iron abundance, tosimulate the effect of adding other metals, the temperature variationsbecome more pronounced.
| Binary Star Speckle Interferometry: Measurements and Orbits
Results of our second observational run of binary star interferometricmeasurements with an ICCD speckle camera attached to the 1.52 mtelescope of the Observatorio Astronómico Nacional at Calar Alto(Almería, Spain) in 2000 June-July are presented. The measuredangular separations range from 0.096" to 6.558". With the use of the newspeckle data, the orbits of the visual binaries WDS 14369+4813 and WDS21597+4908 are improved.
| A Spectroscopic Program to Monitor and Discover A-type Classical Shell Stars
We have embarked on a spectroscopic program to monitor and discover"classical" A-type shell stars. These are late-B, A and early F-typestars which show Fe II and Ti II lines similar in strength to A-typebright giants or supergiants, but their hydrogen lines indicate giant oreven dwarf luminosities. Well known members of the class include 17Leporis and HD 195325. We are particularly interested in stars whichexhibit static shells. We will present preliminary results for thisprogram, including our strategy for discovering new A-type shell stars.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| A photometric catalogue of southern emission-line stars
We present a catalogue of previously unpublished optical and infraredphotometry for a sample of 162 emission-line objects and shell starsvisible from the southern hemisphere. The data were obtained between1978 and 1997 in the Walraven (WULBV), Johnson/Cousins(UBV(RI)c) and ESO and SAAO near-infrared (JHKLM) photometricsystems. Most of the observed objects are Herbig Ae/Be (HAeBe) stars orHAeBe candidates appearing in the list of HAeBe candidates of Théet al. (1994), although several B[e] stars, LBVs and T Tauri stars arealso included in our sample. For many of the stars the data presentedhere are the first photo-electric measurements in the literature. Theresulting catalogue consists of 1809 photometric measurements. Opticalvariability was detected in 66 out of the 116 sources that were observedmore than once. 15 out of the 50 stars observed multiple times in theinfrared showed variability at 2.2 mu m (K band). Based on observationscollected at the European Southern Observatory, La Silla, Chile and onobservations collected at the South African Astronomical Observatory.Tables 2-4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/380/609
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| The continuum re-processing efficiency of Be-star circumstellar discs
We have calculated the total flux emitted in Hα, Pα andBrα by the circumstellar envelope of both an early Be star,γ Cas, and a late Be star, 1 Delphini, assuming the central staris the only source of energy input into the circumstellar envelope.These estimates are based on the Be-star models of Millar &Marlborough which have self-consistent temperature distributionsdetermined by equating the local rates of energy gain and energy loss inthe envelopes. We find that an additional source of ionizing photons, asargued by Apparao, is not necessary to account for the observedemission.
| ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New Orbits
We present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses.
| Speckle Interferometry at the US Naval Observatory. V.
The results of 1544 speckle interferometric observations of 637 binarystars, ranging in separation from 0.25" to 5.25", are tabulated. Theseobservations were obtained using the 66 cm refractor at the US NavalObservatory in Washington, DC, with an intensified CCD detector. This isthe fifth in a series of papers presenting measures obtained with thissystem and covers the period 1998 January 1 through December 31. Randomerrors for all measures are estimated to be 17.6 mas in separation and0.55d/ρ in position angle, where ρ is the separation inarcseconds.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| A-shell stars in the Geneva system
Among the various kinds of A stars having a peculiar spectrum, we findthe A-shell stars. Many questions are still open concerning these stars,including their evolutionary status. In the present study we have useddata from the Hipparcos catalogue to examine this point. We have foundthat the majority of A-shell stars are well above the main sequence. Nodifferences could be established between A-shell stars in luminosityclasses III and I and those in luminosity class V as regardsvariability, duplicity, or the importance of the shell feature.
| Rates of Energy Gain and Loss in the Circumstellar Envelopes of BE Stars. II. 1 Delphini
We have investigated the rates of energy gain and loss in thecircumstellar envelope of the cool B8-9e star, 1 Del, using thePoeckert-Marlborough model. We determined iteratively the kinetictemperature of the gas as a function of position in the circumstellarenvelope by adjusting the temperature at each grid point until the ratesof energy gain and loss there were equal. The gas was assumed to gainenergy from photoionization, collisional de-excitation of bound levels,and free-free absorption, and to lose energy by recombination,collisional excitation, and free-free emission. The resultanttemperatures are a self-consistent solution of the equation of energyconservation. We were also able to reproduce the gross features of theHα line with this model and the corresponding temperature grid.Our investigation demonstrates that there is sufficient continuumradiation present to ionize the circumstellar envelope and produce therelative line strength without any additional source of heating in theenvelopes of cool Be stars.
| Rates of Energy Gain and Loss in the Circumstellar Envelopes of BE Stars: Diffuse Radiation
We have determined an upper limit to the kinetic temperature of the gasin the circumstellar envelopes of two Be stars, a hot star (gamma Cas)and a cooler star (1 Del), by including in an approximate manner thediffuse radiation produced in the envelope. We computed the temperatureas a function of position by balancing at each position the rates ofenergy gain and energy loss. Photoionization, collisional de-excitationof bound levels, and free-free absorption were assumed to contribute tothe rate of energy gain; radiative recombination, collisionalexcitation, and free-free emission contribute to the rate of energyloss. The kinetic temperature at a particular location is obtained fromthe requirement that the rates of energy gain and energy loss there beequal. These results, combined with previous investigations, establishthe range of temperatures expected in the circumstellar envelopes of Bestars if the primary source of energy input is the radiation field ofthe star.
| Speckle Interferometry at the US Naval Observatory. III.
Position angles and separations resulting from 2578 speckleinterferometric observations of 590 binary stars are tabulated. This isthe third in a series of papers presenting measures obtained using the66 cm refractor at the US Naval Observatory in Washington, DC, andcovers the period from 1995 June through 1996 December. Program starsrange in separation from 0.2" to 4.3", with a limiting magnitude ofV=11. Random errors are estimated to be 17.0 mas in separation and0.56d/rho in position angle, where rho is the separation in arcseconds.These are the first results acquired using an improved intensified CCDdetector. The new detector, in concert with an intensity-filteringtechnique applied in software, has permitted a 1 mag increase in dynamicrange, to 3.5 mag, for pairs separated by about 2". The instrumentationand calibration are briefly described, with an emphasis on thecharacteristics of the new detector. The software filter used toincrease the dynamic range is also described.
| Long-term visual spectrophotometric behaviour of Be stars. II. Correlations with fundamental stellar parameters and interpretation
The long-term visual spectrophotometric (SPh) behaviour of Be stars as afunction of fundamental stellar parameters is studied. Some previous SPhresults obtained by other authors are confirmed. Moreover, a tendencyfor temperature and aspect angle dependency of SPh variations is found.From the characteristics of visual SPh behaviour in Be stars we deriveconstraints for models of regions in circumstellar envelopes where thevisual continuum spectrum is formed: (i) The SPh emission and absorptionphases should not imply preferential aspect angles, as they can bothappear whatever the stellar inclination. This phenomenon cannot bealways accounted for by strongly flattened circumstellar envelopes; (ii)Radii of the visible continuum forming regions cannot be larger than afew R_*; (iii) Electron densities of these regions should not exceed N_e~ 10(13) cm(-3) ; (iv) Electron temperature of circumstellar layersproducing the SPh emission phases compare with the stellar Balmercontinuum radiation temperature and it is much lower in those producingthe SPh absorption phases. Three scenarios were studied to produce theobserved characteristics of emissions in the V magnitude and in thesecond component of Balmer discontinuity (Delta D) during the SPhemission phases: (a) expansion of a massive circumstellar shell thatpreserves circumstellar envelope flattening; (b) expansion of acircumstellar shell which increases the global flattening, so that adisc-like structure is formed; (c) continuous mass ejection thatincreases the storage of mass in a constant volume with a givenflattening. Mechanisms (a) and (b) produce a double valued (DeltaV,Delta D) SPh relation, while (c) produces a single valued relation.Only mechanisms (a) and (c) can easily produce the observed amounts ofemission Delta V and Delta D without violating the modeling constraintsfrom (i) to (iv) imposed by observations. The model SPh slopes of (DeltaV,Delta D) show the global sin i and T_eff observed dependencies. Thescenarios used to describe the double valued (Delta V,Delta D) suggestanother possible way how to build up circumstellar envelopes around Bestars.
| Measurements of double stars 1993.67 - 1998.13
624 Micrometer Measurements of 224 pairs with a 32.5 cm Cassegrain, 719Measurements of 310 double stars with a 360 mm Newtonian are given.Tables 1 to 4 are available in electronic form only at the CDS130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| Long-term visual spectrophotometric behaviour of Be stars
The long-term spectrophotometric variations of 49 Be stars are studiedusing the U and V magnitudes of the UBV system, the total Balmerdiscontinuity D and the visible gradient Phi _rb. BCD spectrophotometricand photometric data in five different photometric systems, obtained inmost cases since 1950 and reduced to the BCD system, were used. The(U,D), (V,D), (Phi _rb,D) and (Phi _rb,V) correlations obtained differfrom star to star and they can be single or double-valued. They differclearly for Be phases or Be-shell phases. Be stars with small Vsin ishowing the ``spectrophotometric shell behaviour'': D > D_*, werefound. This finding implies either that strongly flattened models ofcircumstellar envelopes are in doubt for these stars, or that not all Bestars are rapid rotators. Comparison of observed variations with thosepredicted for model Be stars with spherical circumstellar envelopes ofvariable densities and dimensions implies that spectrophotometricpatterns of Be phases are due to circumstellar envelopes in low opacityregimes, while those of spectrophotometric shell phases are due tocircumstellar envelopes in high opacity regimes. In a given star, theenvelope regions responsible for the observed variations of D and Phi_rbin spectrophotometric shell phases seem to be smaller and denser thanthose producing the observed variations of these parameters inspectrophotometric Be phases. The high positive RV found in strong shellphases might favor the formation of compact circumstellar layers nearthe star. Figure 6 is only available in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the structure of Be star disks.
We investigate the geometrical structure of the emitting part ofcircumstellar envelopes around Be stars from an empirical point of view.We use new high-resolution, high-S/N spectroscopic data of the FeIIλ5317 and some other faint FeII emission lines in 27 Be starsshowing symmetrical emission lines (class 1). We find a clearcorrelation between its total width (measuring the maximum velocities ofcircumstellar matter) and the stellar rotational velocity. Thiscorrelation means that a typical Be envelope (or, more precisely, thatpart of it which is visible in optical emission lines) is anaxisymmetric, rotationally supported disk. For empirical investigationof the vertical structure, we use the occurrence of shell lines. Wedefine, as shell criterion based on FeII lines, a Be shell star as onewith FeII central intensity F_cd_/F_*_(FeII)<1. Using this forcalibrating an appropriate parameter for the much more frequentlyobserved Hα line, we find that shell stars are those withF_p_/F_cd_(Hα)>=1.5 where F_p_ is the mean peak intensity atHα. In a sample of 114 programme stars, we find a shell starfraction of 22.8%. This number is readily transformed into a halfopening angle of Be star disks, φ=13deg. We furthermore show thatBe disks must be thin at the inner edge, and may become fairly thick atthe outer rim. This, together with the small value of φ, isevidence for a conical or concave shape, the latter typical of ahydrostatically balanced disk. Finally we provide evidence that thefamous "shell-Be" phase transitions can naturally occur in such disks asa geometrical effect if they are seen under inclination i=~70deg and iftheir outer radius is variable with time.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Hα emission and infrared excess in Be stars: probing the circumstellar disc.
We present near-simultaneous (within one week) high-resolution Hαspectra and near-infrared photometry of 69 B and Be stars. We confirmthat, for the Be stars, the infrared excess and Hα emission arecorrelated, albeit with a rather large scatter. Given thenear-simultaneity of our observations, this scatter probably is notrelated to intrinsic variability, but rather reflects a genuinestar-to-star variation in physical conditions. In order to deriveinformation about the density and velocity structure of Be star discs,we calculate theoretical infrared excesses, Hα equivalent widthsand Hα line profiles for two different models. We find that themodel used by Poeckert & Marlborough (1978a) to fit the spectrum ofγ Cas, is not capable of reproducing the observed correlationbetween the infrared excess and the excess Hα equivalent width,producing - for given infrared excess - Hα emission lines that areweaker than observed. The model of Waters (1986), used successfully tofit the infrared excess continuum emission of Be stars, also fails,producing Hα emission lines that are too strong. We discuss theseresults in terms of the density structure of the wind.
| Radial velocity studies of A-type shell stars.
We have measured radial velocities for a sample of A-type shell stars.We examine the results for the H I, Ti II and Ca II shell lines andcompared them with the radial velocities derived for the underlyingstars. We found that the A-type shell stars reproduce on a smaller scalethe phenomena observed in B-type shell stars.
| On the further observations of BE/shell star V 923 AQL
V 923 Aql is one of the candidate Be stars to be binary star.In this research, optical and near-infrared spectral measurements of V923 Aql is presented. V 923 Aql presents variable H Balmer line profileswith shell components. H alpha profiles present R/V, E/C and radialvelocity variation. Shell parameters of the envelope are calculated.
| A study of Be stars in the wavelength region around Paschen 7
This paper presents a study of the wavelength region 9840 - 10200centered upon P 7 in 74 Be type stars (B0-A0). We find a correlation ofthe P 7 emission with spectral type, the emission being strongest inearly types and disappearing toward A0. All emission lines are doublepeaked. Besides P 7 also several Fe II lines appear in emission, thestrongest being λ 9997. A strong positive correlation existsbetween all emissions and we conclude that Fe II is in emission wheneverP 7 is in emission. P 7 and λ 9997 also show a strong similarityin the details of the line structure. By comparison to stellar radii,the radii of emission-line regions are small and are similar for P 7 andthe Fe II emission lines.
| Multi-wavelength spectroscopy of the stable shell star HD 193182
HD 193182 is one of the most interesting 'stable shell stars' andpresent stable shell features which seems to be constant over decades.In this research we analyzed optical, ultraviolet and near-infraredspectra of this little-studied shell star. In the meantime we appliedmodel calculations to the measured spectral parameters of HD 193182 inorder to present a more complete view of its stellar and envelopecharacteristics.
| The behavior of the O I line 7772 in Be and related stars
We describe the spectra of more than sixty stars in the 7570-7980region. We find that O I 7772 is always in emission in Be stars: in theearliest types it is seen in clear emission whereas in the later typesit fills in the observed absorption line. We find a good correlation ofthe line intensity of O I 8446 with O I 7772, the former being aboutfour times stronger than the latter. We confirm the correlation with FeII 7712. We also derive the outer radii of the line emission formingregions and find that O I 7772 is formed very close to the starssurface, whereas Fe II is formed farther away. We also provide criteriato distinguish, at this wavelength range, the classical Be, Herbig Ae-Beand B(e) stars.
| Lyman alpha emission in spectra of Herbig AE stars - an indication of accretion?
Lyman-alpha emission lines have been detected in the IUE spectra ofseveral Herbig Ae stars, but not in those of Herbig Be stars. The shapesand positions of these lines are not consistent with those expected froma chromosphere and transition region (TR), which may be the origin ofthe other FUV emission lines in the spectra of these stars. The closesimilarity with the Ly-alpha profile of 17 Lep, a low mass binary systemin its first mass transfer phase, that of AE Aqr, a cataclysmicvariable, and those of T Tauri stars suggests that the Ly-alpha emissionof the Herbig Ae stars is formed by recombination of infalling matter.The accretion rates derived from the Ly-alpha fluxes of 17 Lep, AE Aqr,and T Tauri stars are in good agreement with those obtained from otherobservations of these stars. The derived accretion rates of the HerbigAe stars are similar to those obtained for T Tauri stars but 3 orders ofmagnitude lower than those of FU Ori and Z CMa. We have used the profileshapes to constrain the geometry of the infall. The correspondingaccretion energies are amply sufficient to balance the radiative lossesby the other UV emission lines and to drive the outflow from the youngstars.
| Near-IR observations of 101 Be stars
Observations of 101 Be stars taken over a two year period in the near-IRbetween 1 and 5 microns are presented and discussed. The near-IR colorexcess of all program stars is derived, and found to increase withwavelength for all these stars. The fraction of stars with color excessdoubles between 1.25 and 3.6 microns. There appears to be an upper limitto the magnitude of the color excess as a function of stellar type, withearly-type stars having a higher upper limit than later spectral types.No correlation of the presence or magnitude of color excess withprojected rotational velocity is evident. The spectral index of theexcess emission spectra is calculated for stars having color excess. Onaverage, the spectral index through the near-IR and far-IR IRASwavelength regimes is constant. There is evidence that some stars haveexcess emission with spectral index values outside the range expectedfor free-free and bound-free emission. This is attributed to either dustemission or the effect of absorption of photospheric emission by coolcircumstellar material along the line of sight to the star.
| Anomalous infrared emitters among A-type stars
Spectroscopic observations of a sample of 26 stars have been analyzed inthe blue and near-IR to find out if anomalous IR emitters (AIEs) have aspectral signature. It is found that many, but not all, such starsexhibit shell characteristics. Analysis of available IRAS photometricobservations of A-type stars shows that the detection of circumstellarfeatures depends strongly on the number of IR bands at which the objectwas observed. Out of the 707 stars observed by IRAS, 41 AIEs, or 5.7percent, are found. Among nonsupergiant AIEs, 23 percent show shellfeatures. The true percentage of AIEs among A-type stars is estimated tobe 1.5 percent in a volume-corrected sample. A list of 24 stars whichwere apparently not previously detected as AIEs is given.
| AE and A-type shell stars in the near infrared
Spectroscopic observations in the near-infrared of a number of Ae and Ashell stars are presented. It is shown that shells can be detectedthrough the enhancement of the lambda 7773 line and through otherspectroscopic criteria.
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