PROFILE OF AN ESO KEY PROGRAMME Standard Stars for the Infrared Space Observatory, ISO 1 2 1 3 N.S. VAN DER BUEK , P. BOUCHET , H.J. HABING , M. JOURDAIN OE MUIZON , 1, 5 D. E. BLACKWELL 4, B. GUSTAFSSON , P. L. HAMMERSLEy6, M.F. KESSLER~ T.L. UMS, 9 J. MANFROID , L. METCALFE~ A. SALAMA 7

1Leiden Observatory, the Nether/ands; 2 ESO, La Silla; 3Paris Observatory, France; 4 University ofOxford, Eng/and; 5Uppsa/a Observatory, Sweden; 6/AC, Tenerife, Spain; 7ESA-ESTEC, The Nether/ands; 8/mperia/ College, London, Eng/and; 9/nstitut d'Astrophysique de Liege, Be/gium

The Infrared Space Observatory (ISO) volves the use both of internal calibra­ servational programmes, but also es­ is a European Space Agency (ESA) tion sources and a range of astronomi­ tablished a collaboration with Black­ satellite to be launched in 1995. Operat­ cal reference sources (i. e. stars and as­ well's group (Oxford) and with Gustafs­ ing at wavelengths ranging from 2.5 to teroids for the photometrie calibration son's group (Uppsala) to carry out the 200 ~lm (Kessler, 1992), ISO will be a and planetary nebulae or HII regions for theoretical part of the project: determin­ unique facility with wh ich to explore the the spectroscopic calibration). ing fundamental parameters of the stars universe. Its targets will range from ob­ A full description of the plans for the and modeling their far-infrared spectra. jects in the solar system, at one ex­ in-flight calibration of the ISO instru­ The goal of the working group is to treme, to distant extragalactic sourees, ments can be found in the "ISO In Orbit deliver a database of standard stars and at the other extreme. ISO will operate as Calibration Requirements Document", fluxes to the ISO Science Operations an observatory with 65% of its observ­ wh ich is regularly updated by ESA in Team weil before the launch of ISO. ing time open to the general astronomi­ consultation with the instrument con­ cal community. Observations will be sortia. Selecting the Stars selected by proposal submission and peer review. For an efficient calibration of observa­ Stars as Calibrators, the ESO Key The satellite will carry on board a 60­ tions by ISO, i. e. to minimize the slewing Programme cm telescope and four scientific instru­ time of the telescope, there should be at ments, mounted inside a 2300-litre The most suitable sources for the least 1 standard star per hundred superfluid Helium cryostat and operat­ photometrie calibration of ISOCAM and square degrees. In other words, the set ing at a temperature of around 3 K. The the shorter wavelength region of of standard stars for ISO has to contain instruments are: ISOPHOT are stars with well-known at least 400 stars, evenly spread over 1. ISOCAM, a two-channel camera, monochromatic fluxes. Stars can also the sky. operating between 2.5 and 17 Ilm, be used as photometrie standards for In fact, several conditions have to be with a 32 x 32-element detector array SWS and for the short wavelength re­ met by a set of standard stars for ISO. in each channel; gion of LWS, and for correlating SWS Since they will be used as standards for 2. ISOPHOT, a broad-band multi-filter and LWS spectra. However, a different instruments of ISO, the stars photo-polarimeter, covering the homogeneous set of standard stars should cover a wide range of mag­ wavelengths between 2 and 200 Ilm, suitable for wavelengths up to at least nitudes as weil as a wide range of spec­ with a low-resolution spectrometer, 50 ~lm does not exist! tral types. In summary, the setected covering the wavelength ranges 2.5 to The ESO Key Programme, "Infrared stars should be: 5 Ilm and 6 to 12 Ilm; Standards for ISO", is a first step to­ 1. non variable stars; 3. SWS, the short wavelength spec­ wards the setting up of such a system of 2. single stars; trometer, offering resolutions in the standard stars. 3. stars without an infrared excess; range 1000 to 20,000, for In order to make it possible to use 4. brighter than K = 12, and fainter than wavelengths between 2.4 and 44 Ilm; stars as calibrators up to these K = 0; 4. LWS, the long wavelength spec­ wavelengths, their far-infrared f1uxes 5. evenly distributed over spectral type trometer, offering resolutions in the must be known, on the basis of photo­ and magnitude; range 100 to 10,000, for wavelengths metrie and spectroscopic data obtained 6. homogeneously spread over the sky. between 45 and 180 Ilm. from the ground in combination with The ESO Key Programme covers the These instruments are being built by stellar model atmospheres. The aim of observations for the southern hemi­ four independent consortia from ESA this Key Programme is to obtain near­ sphere. We selected stars from the in­ member States, using national funding. infrared (NIR) and mid-infrared (MIR, at frared standard star lists of ESO ESA is responsible for the development 10 and 20 Ilm) photometrie data and NIR (Bouchet et al., 1991), SAAO (Carter, and launch of the satellite, and for the spectroscopic data of the stars selected 1990), AAO (Allen and Cragg, 1983), and observatory operations, which end in the southern hemisphere. Similar CTIO (Elias and Frogel, 1983). We ex­ when the liquid Helium cryogen is ex­ efforts are being undertaken in the tended the sampie by selecting stars hausted, i. e. after a baseline lifetime of northern hemisphere by the IAC from the Bright Star Catalogue (Hoffleit, at least 18 months. (Tenerife) and Imperial College (Lon­ 1982) and the Henry Draper Catalogue. One of the major concerns for such a don). The project, as a whole, runs We used both catalogues and the mission is the calibration of the instru­ under auspices of the ISO Ground Hipparcos Input Catalogue to discard ments and thus of the scientific data Based Preparatory Programme working multiple and variable stars. In addition, products. In addition to the pre-Iaunch group (Jourdain de Muizon and Habing, we used the IRAS catalogue to check on-ground calibration and characteriza­ 1992), wh ich was formed on the initia­ that the spectra of the selected stars do tion of the instruments, the observatory tive of the ISO Science Team. This not show an infrared excess. The sam­ must be calibrated in-flight. This in- working group not only initiated the ob- pie contains 300 stars (see Fig. 1), of 28 - the existing set of standard stars for broad-band NIR photometry will be extended with standard stars having K magnitudes of up to 12;

0 0 - a system of standard stars for o~ 0 narrow-band NIR photometry will be 0 0 . 0 00 0" 0 0 defined; 0 0 .. .. • .1' • - a system of standard stars for MIR ; 0 . •• 0 · 'j> ~m 0 .. photometry at 10 and 20 will be '\, ...... · 0 . .. 0' ·0 declinations smaller than 75°. We will therefore add some stars to the tions. The method is ideally suited for sampie which are located in the polar region. setting up a new photometrie system. For a large data set this method pro­ vides aeeuraeies better than 0.01 mag for the broad-band NIR photometry, and whieh the 200 most suitable stars will predieted by theoretieal atmosphere 0.005 mag for the narrow-band NIR be used as southern standard stars for models. photometry. For the MIR photometry ISO. Clearly this key programme will yield aeeuraeies better than 0.01 mag in Ni several by-produets, whieh are useful and N2, 0.02 in N3, and 0.05 at 00 ean for ground-based work: be reaehed. Photometry For the entire set of stars we are aequiring J,H,K and L broad-band pho- Table 1: The Royal Standard Stars tometry as weil as narrow-band NIR photometry. The narrow-band filters are Spectral type RA (2000) Dec (2000) CVF filters eentred on 1.58 ~lm (H band), 2.16 ~lm (Bry), 2.22 ~m (K band), A-type stars 2.29 ~m (CO) and 3.70 ~m (L band). The HR2421, YGem, Alhena AOIV 06 37 42.7 +16 23 57 use of sueh narrow-band filters im­ HR2491, a CMa, Sirius A1Vm 06 45 08.9 -16 42 58 proves the aeeuraey of the photometry HR3314, C Hya AOV 08 25 39.6 -03 54 23 in two ways: 1. the narrow-band filters HR7069, 111 Her A5111 18 47 01.2 +18 10 53 have pass-bands weil within the atmo­ HR7557, a Aql, Altair A7V 19 50 46.9 +08 52 06 spherie windows: their profiles are not defined by the edges of the atmospherie Early F-type stars windows, and are therefore not ehanged HR0740, 0 Ceti F41V 02 32 05.1 -15 14 41 by variations in the atmospherie trans­ HR5570, 16 Lib FOV 14 57 10.9 -04 20 47 pareney; 2. atmospherie extinetion is HR7469, 0 Cyg F4V 19 36 26.4 +50 13 16 eolour dependent: narrow-band mea­ HR7936, )1' Cap F4V 20 46 05.6 -25 16 16 sures will be less affeeted by extinetion variation than broad-band measures. Solar-type stars Furthermore, the theoretieal interpreta­ HR0098, ß Hyi G21V 00 25 45.3 -77 15 16 tion of narrow-band photometrie data is HR0448 G21V 01 33 42.8 -07 01 31 more straightforward. HR0509, t Cet G8V 01 44 04.0 -15 56 15 Additionally, we are obtaining MIR HRll0l, 10 Tau F9V 03 36 52.3 +00 24 06 photometry at 10 and 20 ~m for the HR1983, YLep F6V 05 44 27.8 -22 26 54 -44 09 07 brightest stars (L:S 2) of the sampie. For HR4903 G1V 12 54 58.4 HR4989 F71V 13 14 14.7 -59 06 12 1O-~m photometry we use the standard HR5996 G4IV-V 16 07 03.3 -14 04 16 filters Ni (1..0 = 8.36 ~m; I.. = 0.85 ~m), N2 (1.. =9.67 ~m; ~A= 1.65 ~m), and N3 0 Red Giants (1..0 =12.89 ~m; ~A=3.7 ~m). We will use these data to investigate the presenee HRl136, b Eri KOIV 03 43 14.8 -09 45 48 of SiO and Sie features in the speetra HR1907, ep 2 Ori KOlllbCN-2 05 36 54.3 +09 17 26 HR2990, ß Gem, Pollux KOlilb 07 45 18.9 +28 01 34 of these stars. The 20-~m photometry HR4232, v Hya K2111 10 49 37.4 -16 11 37 ~m; ~A=5.6 ~lm) (00; 1..0 =18.56 will be HR5340, a Boa, Arcturus K1111bCN-1 14 15 39.6 +19 10 57 used to eheek the far-infrared fluxes as 29 Spectroscopy Fundamental Parameters, Acknowledgements Model Atmospheres and Far IR Up to now we have obtained full We are very grateful to ESO and to the Fluxes IRSPEC spectra in the J,H,K, and L Max-Planck-Institut für Astronomie, bands for 30 stars of spectral type A to We use the NIR photometry as input represented by Professor Elsässer, for K. These spectra are of medium resolu­ for the "Infrared Flux Method" (Black­ the numerous nights of observing time tion (IJ6."- =2 500) and span the follow­ weil, 1986) and determine the effective allocated to this programme. We would ing wavelength regions: 1.05-1 .35 ~lm, temperatures and angular diameters of like to thank the infrared team at La Silla 1.54 - 1.75 fAm, 2.05-2.40 ~lm and the stars. Independently we shall deter­ for their assistance during the obser­ 3.45-4.05 fAm. To cover these four at­ mine effective temperatures and vations, with our special thanks to mospheric windows, a total of 63 gravities of the stars by comparing the Rolando Vega. We also thank C. Turon IRSPEC spectra need to be taken for observed and theoretical infrared col­ and D. Morin for helping us with the each star. They are the first complete ours, as described by Bell and Gustafs­ Hipparcos Input Catalogue before publi­ stellar spectra taken in the J,H,K and L son (1989). To be able to compare the cation. bands and they will provide new con­ NIR data obtained at ESO with theoreti­ straints on the modeling of stellar atmo­ cal infrared colours, we will extend the spheres. We reduce the spectra with work by Bell and Gustafsson for both MIDAS and routines especially de­ the ESO J,H,K and L filters and the References veloped for the reduction of IRSPEC narrow-band NIR filters, described be­ Allen, DA, and Cragg, T.A., 1983. MNRAS, data (see also the article by R. Gredel in fore. 203,777. this issue of the Messengel). We will use the fundamental parame­ Bell, R.A. and Gustafsson, B., 1989. MNRAS, ters as input for model atmospheres: 236,653. recent versions of the Kurucz models Blaekwell, D. E., Booth, A.J., Petford, A. D., The "Royal Standard Stars" (Kurucz, 1991) for the hotter stars, and Leggelt, S. K., Mountain, C. M. & Selby, The prediction of absolute fluxes of recent models from the Uppsala model M.J., 1986. MNRAS, 221, 427. these standard stars will be subject to atmosphere codes (updated versions of Bouehet, P., Manfroid, J., Sehmider, F.-X., severe uncertainties in model atmo­ Gustafsson et al., 1975, with the Kurucz 1991. A&ASS, 91, 409. Carter, B.S., 1990. MNRAS, 242, 1. spheres. These uncertainties, which [1991] atomic line lists implemented) for Elias, J. H., Frogel, J.A., Hyland, A. R. and may lead to systematic errors in the the cooler stars. We will extend model Jones, T.J., 1983. ApJ, 88,1027. calibration of ISO fluxes of more than atmosphere codes into the infrared, and Gredel, R., 1992. The Messenger, 70, 62. 10%, are in particular errors in funda­ use them in combination with the NIR Gustafsson, B., Bell, RA, Eriksson, K., mental parameters, in temperature data to predict infrared fluxes for the Nordlund, A. 1975. A&A, 42, 407. structure and in continuous and complete set of standard stars. The HoHleit, D., 1982. The Bright Star Catalogue molecular opacities. In order to get a stars with K > 6 will be used as a (4th revised edition), Yale University Ob­ handle on these uncertainties, we are standard system for the short servatory, New Haven. Salama, A. and Metcalfe, L., 1992. ISO In studying the effects of perturbations of wavelength range of ISO, up to 20 ~lm. Orbit Calibration Requirements Document: the above-mentioned parameters on the The stars with K :5 6 will be used as ISO - SSD - 9003, Issue 1.0, 01-07-92. far infrared spectra of model atmo­ calibrators up to at least 50 fAm. Jourdain de Muizon, M., Habing, H. J., 1992. spheres. To improve the calibration, we The aim of the project is to predict the In Infrared Astronomy with ISO, eds. also will make a detailed comparison of infrared fluxes of the complete sampie Th. Enerenaz and M. F. Kessler (New York: observed and synthetic spectra and of stars, with accuracies better than Nova Seience), p. 129. fluxes of a sampie of stars, selected to 10% for flux densities ;::: 1 Jy and to Kessler, M.F., 1992. In Infrared Astronomy be representative for the full set of stan­ compile a list of standard stars which with ISO, eds. Th. Enerenaz and M. F. dard stars. We selected 22 such stars, are suitable for wavelengths up to Kessler (New York: Nova Seience), p. 3. Koornneef, J., 1983. A&A, 128, 84. named "Royal Standard Stars": 5 A-type 50 ~lm. The working group plans to Kuruez, R. L. 1991. In lAU Symp. 149: The stars, 4 early F stars, 8 solar-type stars deliver a database of standard stars stellar populations ofgalaxies, eds. B. Bar­ and 5 K giants (see Table 1). These Roy­ and infrared fluxes to the ISO Science buy and A. Renzini (Dordreeht: Kluwer al Standard Stars will serve as a basic Operations Team weil before the Aeademie Publishers), p. 225. set for checking the calibration of the launch of ISO, presently scheduled Manfroid, J. 1985. Habili!. Thesis, Universite entire sampie of standard stars. for 1995. de Liege.

SUSI Discovers Proper Motion and Identifies Geminga

2 1 G.F. BIGNAMI , 1, P.A. CARAVEOL 1 and S. MEREGHETTI 11stituto di Fisica Cosmica deI CNR, Milano, Italy; 20ipartimento di Ingegneria Industriale, Universita di Cassino, Cassino, Italy

Twenty years have gone by since the this puzzling object first in the y-ray using all the big telescopes of the world. discovery of the y-ray source 195+5, the domain, with the ESA COS-B satellite Unfortunately, every step down in ener­ first UGO (Unidentified Gamma Object) (1975-82), then in the X-ray domain, gy cost a factor of 1000 in the source seen by the NASA SAS-2 satellite. with the NASA Einstein Observatory strength (see table) and, adjusting the These years have been characterized by (78-81) and ESA EXOSAT (83-86) mis­ observing time, we ended up with an endless quest for an identification of sions, finally in the optical (1983-today) -1000 photons in each energy range. 30