Maria Massi
                                                                  Max Planck Institut für Radioastronomie

                                                                                 Millimeter and Submillimeter Astronomy Group
1.  Curriculum

2.  Teaching  Activity
Lectures Winter term
Lectures Summer term

3.  Scientific Activity

                        Stellar Coronae
Physical mechanisms  of the  radio continuum emission from stars
Theory of the very-long-baseline-radio-interferometry  data analysis

4.  Public Outreach
Schülerpraktika (Bonn, Germany)
Monteprandone sotto le stelle (Monteprandone, Italy)
Max-Planck-Institut für Radioastronomie
Auf dem Hügel 69, D-53121 Bonn, Germany
Fax: +49 228 525 435
Office: Room 2.30 Tel: +49 228 525 245 

Conference: "Steady Jets and Transient Jets"

Conference: "Coronae of Stars and Accretion Disks"


Personal record
Name: Maria Massi  
Nationality: Italian
Marital status: Married, 2 Children


Laurea  in Physics                                  University of Rome, Italy.
Ph. D. in Astronomy                               University of Bonn, Germany.
P. Dozentin (Habilitation) in Astronomy  University of Bonn, Germany.


- date  Teacher at the University of Bonn. Course I : Astrophysics of Microquasars.  Course II :  Stellar Coronae

2000 - date  Researcher at the Max Planck Institut für Radioastronomie  (MPIfR , Bonn, Germany)
  JIVE Support Scientist (Joint Institut for VLBI in Europe, Dwingeloo, The Netherlands) at the MPIfR

   Researcher at  the Osservatorio Astrofisico di Arcetri (Florence, Italy)

CNR Fellowship (Consiglio Nazionale delle Ricerche)  at the MPIfR, Bonn

            NATO Fellowship, University of Washington (Seattle,USA)

- Member of the Scientific Organizing Committee for the Conference "Radio emission from the Stars and the Sun." (Barcelona, 1995).
- Member of the Technical and Operations Group (TOG) for the European VLBI Network (EVN): subgroup Operations(1998-1999).
- Proposed for the"Marie Curie Excellence Award"  2003-2004 of the European Union  from Prof. G. Tofani (Director of the Istituto di Radio Astronomia, Bologna) and Prof. K. Menten (Director at Max-Planck-Institut für Radioastronomie, Bonn).
- Chair of the Scientific Organizing Committee for the Conference "Coronae of Stars and Accretion Disks" (Bonn, 2006).

The scientific activity   of Maria Massi developed  in two distinct, but connected, areas: on one part in astrophysics (i.e. microquasars, stellar coronae and physical mechanisms of the radio continuum emission from stars) and on  the other  in astrophysical techniques (i.e. Radio-interferometry).  The  results of the research in both fields have been published in 93 publications so distributed: 40 articles in refereed journals, 15 technical reports, 38 proceedings.
  Articles in refereed Journals
Articles in Conference Proceedings
  Technical  Reports


Teaching Activity
I.  Quasars and Microquasars

  Quasars  and Microquasars
  Thursday  13-15, HS 0.01, MPIfR
  Instructor: Maria Massi

Stellar-mass black holes in our Galaxy mimic many of the phenomena  seen in quasars  but at much shorter timescales. In these lectures we present and discuss how the simultaneous use of multiwavelength observations has allowed a major progress in the understanding of the accretion/ejection phenomenology.

  Chapter  1
   Microquasars and Quasars   
   Stellar evolution, white dwarf, neutron star, BH

  Chapter 2   
   Accretion power in astrophysics
   Eddington luminosity
   Temperature of the accretion disc
   Low and High Mass X-ray Binaries
   Accretion by wind or/and by  Roche lobe overflow
   Mass function: neutron star or black hole?

  Chapter 3
     X-ray observations
     Spectral states
     Quasi Periodic Oscillations (QPO)

  Chapter 4
     Radio observations
     Single dish monitoring and VLBI
     Superluminal motion  (review, article)  
     Doppler Boosting    
     Synchrotron radiation
     Plasmoids and steady jet

  Chapter 5



  II.  Stellar and Solar Coronae  

 Stellar and Solar Coronae
 Thursday  13-15, HS 0.01, MPIfR
 Instructor: Maria Massi

T Tauri  (young stellar systems not yet in Main Sequence) and RS CVn systems (evolved stellar systems that already left the Main Sequence), although very diverse systems, have similar flare activities observed at radio and X-ray wavelengths.

The flares in both systems are several orders of magnitude stronger than those of the Sun.  The origin of this activity, defined "coronal activity", depends on the convective zone, the rotation, the formation and dissipation of magnetic fields. In general terms: This is a mechanism of the same type as on the Sun, but enforced by the binary nature of these systems.

In these lectures we will explore a link between the amplification of initial magnetic fields by dynamo action in several rotating systems ( Sun, binary systems and accretion discs around black holes) and the release of magnetic energy into a corona where particles are accelerated.

Together with the basic theory  there will be as well illustrated the latest progress in the research on stellar coronal emission derived from recent space missions and high-resolution radio observations.
Solar Cycle: Observations
Solar Cycle: Theory                  
Flare theory
The standard model of the solar flares
Physical Processes
Stellar Coronae  





Scientific Activity

I.  Microquasars

Microquasars are stellar binaries, where a collapsed object (black hole or neutron star) accretes material from a normal star.  As compared with a quasar (with black holes up to 10^9 solar masses)  the microquasar's  black hole (of a few solar masses) is surrounded by a smaller (of 9 order of magnitude) accretion disk and produces a smaller jet,  yet relativistic. Several  phenomena relative to the accretion process in quasars, occur as well in a microquasar, but at much shorter time scale (hours/days instead of years).
That explains the big interest attributed recently to these objects.

The microquasars are a selected class of the X-ray binaries.That are  systems well known since the 1960s:  the X-ray emission originates from the very hot accretion disk surrounding the compact object. However, it took a long time to discover that some of  these systems also have relativistic radio jets. For several years, after its discovery on 1979, SS 433 with  its spectacular jets was thought to be a unique case. After  the discovery of a second source ( Cyg X-3) several groups (including us) in the 1990s started to search for new X-ray binaries with radio emitting jets.

LS I +61 303

 Fig. 1

  LS I +61303 is one of the most observed Be/X-ray binary systems because,  peculiarly, it has   periodical radio and X-ray emission together with  strong,  variable gamma-ray emission.
The binary stellar system has an orbital period of 26.496 days and a rather eccentric orbit  (e=0.7). The visible companion is an early type, rapidly rotating B0Ve star. Be stars have a dense and slow  disk-like wind with a wind density distribution following a power law. Through this dense, structured and variable envelope  the compact object (black dot on the orbit in Fig. 1) travels and accretes.

The accretion rate in an eccentric orbit has two peaks: One peak corresponds to the periastron passage because of the highest density;
the second peak occurs  around apastron where the drop in the  relative velocity of the compact object compensates the decrease in density. For supercritical accretion,  theory predicts matter be  ejected outwards in two jets perpendicular to the accretion disk plane. However,  near periastron  the ejected relativistic electrons  are embedded in such a strong UV-radiation field  that they loose completely their energy by inverse Compton  process (gamma-ray emission is observed   but no radio emission). During the second accretion peak, the compact object  is much farther away from the Be star and both, inverse Compton losses and wind opacity, are lower: The electrons can propagate out of the orbital plane and   radio outbursts are observed.The radio emission has been resolved with VLBI, EVN and MERLIN observations and in agreement with the theoretical predictions the image shows bipolar jets emerging from a central core (see  articles  18,21,24,27,32,36,37,39; conf. proc. 12,15,19,27,31,33,35,36,38)

LS 5039

Most of the known microquasars were  discovered after a noticeable X-ray outburst (observed by satellites) that triggered the detection  of the radio-jet with ground based telescopes. Our procedure, led by Paredes of the University of Barcelona,was different. We performed high resolution radio observations (VLBA)  of a selected sample of  sources determined by a systematic cross-correlation between public archives of data in the X-ray, radio and optical domains under restrictive selection criteria.

The VLBA map of the resulting candidate LS 5039 proves that the radio structure  is that of bipolar jets emanating from a central core. The presence of radio jets in this  X-ray binary is the main evidence of an accretion process resulting in the ejection of relativistic particles.  The overall length of the source is about 18 AU. The stronger jet is interpreted as an approaching Doppler-boosted jet of a symmetric pair.  Almost simultaneously with that observation, the publication of the third EGRET catalog (Hartman et al. 1999) allowed us to search for a possible counterpart  at higher energies: As a result we found a coincidence of LS5039 with the gamma-ray source 3EGJ1824-1514. (articles 31, 34, 35; conf. proc. 20,21,22,23,25,26,28, 29,30,34)


II.  Stellar Coronae        

Magnetic configuration and mechanisms of stellar flares

The dynamo theory  (Parker 1955) explains how differential rotation  generates a toroidal field in the  interior of a star from an initial stellar  dipole field, and how convection,  bringing up this field  to the surface, creates the coronal magnetic arc-like structures called loops. Whereas  the Sun's global dipolar field  is of only a few gauss the loops are  "islands" of enhanced magnetic fields reaching  at their photospheric footpoints (sunspots) thousands of gauss.

There exists  a close relationship between magnetic loops and  flares.  In fact, as  observed on the Sun, flares are triggered by interactions between new and older emergences of magnetic flux in the same area (Nishio et al. 1997). The released  magnetic energy   accelerates a part of the thermal electrons trapped in the loops to high energies causing the flare (Priest & Forbes 2002).

RS CVn and T Tauri  systems  are  characterized by intense (orders of magnitude higher than the Sun) coronal activity at X-rays, UV and radio wavelengths.  Long time monitorings of the radio  flux density  of  RS CVn and TTauri systems, performed with the Effelsberg 100-m telescope,  have  shown the presence of  periodicities in the flaring activity of  UX Arietis and  V773 Tauri  (articles 19, 25, 33,38).
This  observational finding has opened the question if the periodicities could be due to an inter binary collision (therefore depending on the binary nature of UX Arietis and V773 Tauri)  or instead  due to an intrinsic mechanism originating in the stellar interior (and therefore also common to other stars).

UX Arietis

 The process causing the emerging of the loops is the dynamo working in the star's interior.  However, Rossby-type waves might modulate the emergence of  magnetic flux (Lou 2000). In this respect , periodic emergence of magnetic flux through the photosphere may operate in two different ways, either forming spots within already established  active regions (and therefore inducing  periodic flares by magnetic reconnection) or by forming new spots away from active regions(Ballester et al. 1999) .

The Rieger periods are solar cycles with a time scale of months, which are present  in both  flaring activity and  sunspot occurrence.
These short-term periodicities
are considered a peculiar and not yet fully understood solar phenomenon  (Ballester, Oliver and  Carbonell 2002).

We performed a timing analysis of two 9-year datasets of radio and optical observations of UX Arietis (art. 38). The analysis reveals  a 294-day cycle. When  the two 9-year datasets are folded with this period, synchronization of the peak of the optical light curve (i.e., the minimum spot coverage) with  the minimum  radio flaring activity is observed (Fig.  2). This close relationship between  two completly independent curves makes it very likely that the  294-day cycle is real.  We conclude that the process invoked for the Sun of a periodical emergence of  magnetic flux may also be applied to UX Arietis  and can explain the cyclic flaring activity  triggered by interactions between successive cyclic  emergences of magnetic flux in the same area.

Fig 2. UX Arietis
Folding of  the radio and photometric V data with  a period of 294 days.

Bottom: Folding of  the radio  data with  a period of 294 days.The phase interval 0--1 is repeated twice.There is a clear lack of energetic flares at phase 0.4. Top: Folding of the photometric V data with the same period of 294 days, as the radio data. The data are averaged over phase bins of 0.01. The peak for V at  phase 0.4  corresponds to a minimum in spot coverage and is well synchronized with the ``hole'' of radio flaring activity.

V773 Tauri

Fig. 3. V773 Tauri
Top: Flare observed at periastron passage with the PdBI.
sketch of the binary system.

The system V773 Tau is composed of two stars orbiting with a period of 51.075 days. In the sketch of Fig. 3  one star is plotted in the focus of the slightly eccentric orbit, the other star is shown at three different positions along the orbit.

A  periodicity   in the radio flaring activity, evident during the Effelsberg 100-m  telescope monitoring, was  confirmed by a dominant peak at 52 \pm 5 days in the Fourier  power spectrum. Folding the data with the orbital period of 51.075 days the flares cluster at the periastron passage. The detailed monitoring  around one periastron passage with the VLA and with the Effelsberg telescope  reveals a modulation of the radio emission  in agreement with the 3.4 days rotational period of the star spots, observed in the optical range. A possible  scenario explains the 52 days periodicity  and the  3.4 days modulation with  recurrent interactions  of giant magnetic structures, anchored on the  two rotating  stars of the  system, consecutively colliding for two or three rotations  during each  periastron passage (art. 33).

We have observed such  a flare at a wavelength of 3 mm  (art. 40). We rule out that the fast fading of the emission  can be due to  energetic losses (i.e. synchrotron, collisional and inverse Compton losses) of the emitting electrons and propose  that it is due to the leakage of  the emitting electrons themselves at each reflection between the two mirror points of the  magnetic structure partially trapping them. The magnetic structure compatible with the leakage model is that of an  helmet streamer that, as in the solar case, may occur at the top of X-ray emitting stellar-sized coronal loops of one of the stars. Interpreting the  rising time of the flare of Fig. 3  in terms of propagation towards the low corona of a shock due to  a magnetic reconnection event occurring at large height, we  have determined a  height compatible with periastron distance.
Therefore, the streamer may  interact with the corona of the other star at periastron passage, causing  recurring flares.The inferred  magnetic field strength at the two mirror points of the helmet streamer is in the range 0.12 - 125 G and the corresponding  Lorenz factor of the partially trapped  electrons results to be 20 < gamma < 632.  We therefore rule out that the emission could be of gyro-synchrotron nature: the derived high  Lorenz factor proves  that the nature of the emission at 90 GHz from this pre-main binary system is  synchrotron radiation.


III.  Physical mechanisms of the radio continuum emission from stars

Investigations on the conditions which produce continuum radio emission from the stars, and on the characteristics of the emission (thermal and non thermal) have been performed. The study includes not only "normal" stars (i.e. appearing in  the classical Hertzsprung - Russel diagram) of  early and late type, but also pre-main sequence stars and compact objects (as neutron stars and black holes).

 Ionized envelopes around stars of early spectral types, winds and ultra compact HII regions, have been investigated, and the specific differences of the two types of emission (i.e. different spectral index, different density distributions, etc.) have been analysed (see articles  2,3,4). In the star forming region  M17 beside winds and ultra compact HII regions other sources have been identified, which suggest to be neutral clumps surrounded by ionized (from external stars) envelopes (art. 5). This  suggestion has been  proved by a  later observation in the (1,1) ammonia line (art. 8). Other sources in the core of the Orion nebula having thermal spectra as well but not fitting any of the above models  are  explained  as protostellar disks, of optically visible  low mass stars, ionized by external stars  (art. 7). In conclusion the basis of the radio continuum emission of all these type of sources, beside specific differences, is  the same physical mechanism: The radio emission  is due to electrons with a Maxwellian velocity distribution, deflected in the coulomb fields of ions (i.e. free free).

Depending on the presence and  strength of a magnetic field, accelerations due to encounters of electrons with ions can become  negligible in comparison with those due to gyration around the field lines. Trapped in the magnetic loops of stellar systems,  electrons with Maxwellian   distributions are able to produce gyro synchrotron radiation. However, often the characteristics of the  spectra cannot  be fitted with   a Maxwellian  distribution because this would imply too strong magnetic fields (papers 11, 17).  For realistic values of B this corresponds to the case of enough high energetic  electrons with rare collisions; in this case a non-Maxwellian tail is dominant and the distribution is described by a power law  (art.  9, 26). In the case of mildly relativistic particles we observe gyro synchrotron radiation, while for high  relativistic particles the observed emission is synchrotron.

Which  physical processes  are able to accelerate  the electrons to high energy ?

Electrons can be  accelerated to quasi relativistic energies  by magnetic reconnection in  binary systems of RS CVn type; this occurs if two fields of opposite directions are pushed one against the other as in the case  of emerging loops intruding from below the stellar surface into other loops already established. In one of the most active RS CVn systems, UX Arietis, high resolution radio measurements (by VLBI techniques) have been  fitted with models of intruding loops (art. 28, 29; conf. proc. 32). The process causing the emerging of the loops is the dynamo working in the star's interior. At the best this can be  studied by long time monitoring of the flux density; that is the reason for the monitoring program of RS CVn and TTauri stars with the Effelsberg 100-m telescope  art. 19, 25, 33). We note that  the first class include  late type stars, while the TTauri are pre-main  sequence stars. The common  characteristic of the two classes of stellar systems  is the presence of a deep convective zone in both: the main ingredient for the dynamo to work.   Periodicities have been discovered in UX Arietis and the TTauri system V773 Tau (art. 25,33 and 38).    This  observational finding has opened the question if the periodicities could be due to an inter binary collision (therefore depending on the binary nature of UX Arietis and V773 Tau)  or instead  due to an intrinsic mechanism originating in the stellar interior (and therefore also common to other stars).
 Other mechanisms of  electron acceleration are by means of collisions between the winds of the components of a binary system, as proposed for the WR star HD 193793  (art. 15, 16; conf.  proc. 8) or by means of  super accretion processes around compact objects as neutron stars or black holes, accreting from a normal companion.  In this last class of objects, called microquasars, the morphology of the radio emission is that of a double relativistic jet  (orthogonal to the accretion disk of the compact object) as  in LS I 61303 and LS 5039 (see sec. I).

IV. Theory of the Very-Long-Baseline-Interferometry data analysis.

The lack of phase information had prevented VLBI from being a true imaging technique until Rogers and his co-workers (1974) applied a phase closure relationship. The introduction of the closure phase concept marks the beginning of a new era in VLBI. Many authors developed methods,  reviewed by Pearson and  Readhead (1984), which  explicitly or implicitly use this quantity. In paper 10 I  show how the methods  explicitly using the closure phase can be unified in one equation. In one attempt to unify all methods together we have found that all  methods turn out to be  particular cases of the method proposed by Schwab (1980) depending on a proper scheme of  baseline  weighing (art. 12).

By using   Schwab's method,   called self-calibration,a map of the radio source can be obtained by using an algorithm  which includes fourier transform and CLEAN, following an iterative  procedure first indicated by Readhead and Wilkinson (1978) and called Hybrid mapping. That this procedure can converge on wrong solutions has been pointed out by many authors in the past: Walker (1986) indicated the bias in the resultant data due to the use of a point source as starting model. Baath (1989) suggested the use of the original data set  in each iteration of self calibration. Linfield (1986) analysed the role of the (u-v) coverage and lack of intermediate spacing. Generally,  the full procedure to avoid false features is  not clear and only experience with imaging helps  the user to avoid them.

In paper 30 we  have   demonstrated that the problem is connected with the non-linear nature of self calibration which leaves initial wrong assumptions frozen in the final solution. We demonstrated that the general precondition to avoid false structures in the map is that the errors (or more precisely their cube) of the model should  be smaller than the observed  closure phases. This condition, generally satisfied  for a standard earth based array, is violated if  one telescope of the array is very displaced from the others, as it is for an array including one telescope mounted on a satellite.

Using self calibration  it is  assumed that the baseline based errors are negligible. In spite of the fact that these baseline errors are quite small their effect on the map's quality is rather serious. Tests were performed to determine at which level errors limit the obtainable dynamic range with the VLA (Perley 1986)  and  with the VLBA (Briggs et al. 1994).
 For the  European VLBI Network (EVN)  such an analysis  has been developed by myself and  my collaborators  (art.   22, 23; conf. proc. 6,7; tech. reports 10, 11, 14). The result of our analysis was that the  cause  of the low dynamic range of the EVN maps was the  large instrumental polarization  ("D" terms) at many European telescopes.  The correction of the  D terms  has been always disregarded  in the past because they were assumed to be  negligible   and because they affect the data at the second order only. On the contrary,  our analysis and monitoring have shown that: 1) the instrumental polarization is quite large (up to 20%) and presents an unexpected strong frequency dependence (see Fig. 1),     2) its removal led to  an improvement in the dynamical range of the images up to a factor 7.
As a result of this work the international software AIPS released at Socorro (USA)  has been changed to apply this correction. The updated versions of AIPS to use are those with release 15OCT96 and later.

Fig. 1: Plots of the left D-term amplitude (1=100%) for various EVN telescopes (6cm  network monitoring experiment C-1997-C1A) as a function of frequency. The symbols are described in the plot legend (see Massi & Aaron   EVN-Doc 77)


Monteprandone sotto le Stelle
Maria Massi,  Jürgen Neidhöfer,  Egidio Zennaro, Eulalia Romandini
in collaborazione con la locale Associazione PRO LOCO

Conferenze Astronomiche e Osservazione col Telescopio
Monteprandone                                                               Conferenza   (ore 21:00)
                                                                           Osservazione astronomica 
  (ore 22:30)

1.  Il sistema solare  (29 Dicembre 2002)           

2.  La nostra Galassia  (6 Settembre 2003)

3.  Il Big-Bang  (12 Aprile 2004)

4.  Buchi neri e Quasar (17 Aprile 2006)

5.  Come nascono le stelle ? (Agosto 2007

6.  Microcosmo macrocosmo  (22 Luglio 2008)

7.  Dal Big-Bang all'uomo  
(1 Agosto  2009

8.  Stelle cadenti  (11 Agosto  2010
9.   Dal sistema solare ai confini dell'Universo   ( 24 Luglio  2011)


Articles in Refereed Journals

40)"Synchrotron  emission  from  the T Tauri binary system V773 Tau A"
M. Massi, J. Forbrich,K. M. Menten, G. Torricelli-Ciamponi , J. Neidhöfer,S. Leurini  and F. Bertoldi
2006, AAaccepted
39)"Introduction to Astrophysics of Microquasars"
M. Massi.
Habilitation Thesis, June 2005, University of Bonn, Germany 2005, astro-ph/0506731

38)"Discovery of Solar Rieger periodicities in another star"
M. Massi, J.  Neidhöfer, Y.  Carpentier and  E. Ros
2005, AA, 435, L1
37)"LS I +61°303 in the context of microquasars"
Massi, M.
2004, AA, 422, 267
36)"Hints for a fast precessing relativistic radio jet in LS I +61°303"
Massi, M., Ribó, M., Paredes, J. M., Garrington, S. T., Peracaula, M. and Martí, J.
2004, AA, 414, L1
 35)" EVN and MERLIN observations of microquasar candidates
at low galactic latitudes "
M.  Ribó,  E. Ros,  M. Paredes,   M.  Massi,  J. Martí A&A, 394, 983    (2002)
34)"Confirmation of persistent radio jets in  the microquasar LS 5039"
J. M. Paredes,  M.  Ribó,  E. Ros, J. Martí,  M.  Massi A&A   Letter, 393, 99 (2002)
33)"Periodic radio flaring on the T Tauri star V773 Tauri"
M. Massi, K. Menten, J. Neidhöfer A&A, 382, 152  (2002)
32)"One-sided jet at milliarcsecond scales in LS I +61303"
M. Massi, M. Ribo, J. M. Paredes, M. Peracaula, R. Estalella A&A , 376, 217  (2001)
31)"Discovery of a high-energy gamma-ray-emitting persistent microquasar"
J. M. Paredes, J. Martí, M.  Ribó, M.  Massi Science, 288, 2340 (2000)
30)"Space VLBI and Spurious Symmetrization"
 M. Massi, S.  Aaron A&A Suppl. Ser., 136, 211 (1999)
29)"Flaring loop structures at VLBI scale in UX Arietis"
 E. Franciosini, M. Massi, J.M.  Paredes, R. Estalella
 A&A, 341, 595 (1999 )
28)"Investigation of stellar loop structures using VLBI"
 M. Massi, E. Franciosini, J.M.  Paredes, R. Estalella
New  Astronomy Reviews, 43, 539 (1999)
27)"Milliarcsecond radio structure of LSI+61 303"
 J. M. Paredes, M.  Massi, Estalella R., M. Peracaula
A&A, 329, 951 (1998)
26)"Radio flares from the active binary system UX Arietis"
G. Torricelli, E. Franciosini, M. Massi, J. Neidhöfer
 A&A, 333, 970 (1998)
25)"Activity Cycles in UX Arietis"
M. Massi, J. Neidhöfer, G. Torricelli-Ciamponi, F. Chiuderi-Drago
A&A, 332,14 (1998)
24)"Deep VLA images of LSI+61303: a search for associated extended radio emission "
J. Marti , M. Peracaula ,J.M. Paredes , M. Massi ,R. Estalella
A&A, 329, 951 (1998)
23)"Baseline errors in European VLBI Network measurements III.
M. Massi,  M. Rioja,  D. Gabuzda,  K. Leppanen, H. Sanghera, K.  Ruf, L. Moscadelli
A&A, 318, L32 (1997)
22)"Baseline errors on European VLBI Network measurements II. Instrumental Polarization"
M. Massi, G. Comoretto, M.  Rioja, G. Tofani
 A&A Suppl., 116, 167 (1996)
21)"A search for near-infrared variability in LSI+61303"
L. K. Hunt , M. Massi ,S. A. Zhekov
A&A, 290, 428 (1994)
20)"Critical density for magnetic decoupling: preliminary observations"
M.  Massi , S. Lizano
A&A, 287, 581  (1994)
19)"Periodicities in the Radio Emission of UX Arietis ?"
J. Neidhöfer , M. Massi , F.  Drago
A&A, 278, L51, (1993)
18)"High resolution radio map of the X-ray binary LSI+61303"
 M. Massi ,  J. M. Paredes , R. Estalella , M.  Felli
A&A, 269, 249 (1993)
17)"Quiescent Radio Emission in UX Arietis"
M. Massi, F. Chiuderi-Drago.
A&A, 253, 403 (1991)
16)"Intercontinental VLBI observations of theta 1 Orionis A"
M. Felli, M. Massi, M. Catarzi.
A&A,  248,453 (1991)
15)"VLBI observations of HD 193793"
M. Felli, M. Massi
A&A, 246, 503 (1991)
14)"Baseline errors in VLBI measurements"
M. Massi, G. Tofani, G. Comoretto.
A&A, 251, 732 (1991)
13)"The H2O maser Arcetri atlas".
G. Comoretto, F. Palagi, R. Cesaroni, M. Felli, A. Bettarini, M. Catarzi,G. P. Curioni, S. Di Franco, C. Giovanardi, M. Massi, F. Palla, D. Panella, E. Rossi, N. Speroni, G. Tofani.
A&A. Suppl. Series, 84, 179 (1990)
12)"Recovery of phase information from radio-interferometric observations".
M. Massi, G. Comoretto.
A&A, 228, 569 (1990)
11)"High resolution radio observations of theta 1  Orionis A"
M. Felli, M.  Massi, E.  Churchwell.
A&A, 217, 179 (1989)
10)"Application of Lagrangian multipliers in hybrid mapping "
M. Massi
A&A, 208, 392 (1989)
9)``VLBI observations of RS CVn and Algol-type binaries."
M. Massi, M.Felli, R. Pallavicini,F. Palagi, G. Tofani, M. Catarzi.
A&A,197, 200 (1988)
8)"Small scale clumping in M17"
M. Massi, E. Churchwell, M. Felli
A&A, 194, 116 (1988)
7)"Solar system sized condensations in the Orion Nebula"
E. Churchwell, M. Felli, D Wood,  M. Massi
ApJ, 321, 516 (1987)
6)"Radio continuum observations of the blister type HII region  in MonR2"
M. Massi , M. Felli, M. Simon
A&A, 152, 387 (1985)
5)"A high resolution study of M17 at 1.3, 2, 6 and 21 cm"
M.Felli, E.Churchwell, M. Massi
A&A, 136, 53 (1984)
4)"High spatial resolution observations of S106 from 0.6 micron to 1.3 cm.  A wind model for the bipolar nebula"
M.Felli, J.Staude,Th. Reddmann,M. Massi, C. Eiroa, H. Hefele,Th. Neckel and N. Panagia
A&A, 135, 261 (1984)
3)"Star formation in the M8E region"
M. Simon, L. Cassar, M. Felli, J. Fischer, M. Massi,  D. Sanders
ApJ,  278, 170 (1984)44
2)"Infrared line and radio continuum emission of circumstellar ionized  envelopes"
M.Simon, M.Felli, L.Cassar, J.Fischer, M. Massi
ApJ, 266, 623 (1983)
 1)"Long-baseline interferometry of compact radio sources at 18 cm"
L. Matvejnko, B. Kostenko, A. Papaczenko, N. Bartel, M. Massi, J. Romney,K.Weiler,A. Ficarra, F. Mantovani,L. Padrielli, I. Moiseev, L. Both,T. Nicolson
 Soviet Astronomy Lett.,  7, 259 (1981)

Articles in Conference Proceedings

38)"The gamma-ray emitting microquasar LS I +61 303"
Massi, M., Ribó, M., Paredes, J. M., Garrington, S. T., Peracaula, M. and Martí, J.
2005, AIPC, 745,311
37)"The Massive Young Stellar Triple Theta1 Orionis A"
Petr-Gotzens, M. G.  and  Massi, M.
2005, Protostars and Planets V, Proceedings, p.8173
36)"The periodic microquasar LS I +61°303 in the radio and gamma-ray bands"
Massi, M., Ribó, M., Paredes, J. M., Garrington, S. T., Peracaula, M. and Martí, J.
  2005, MmSAI, 76, 96
35)"Radio-loud and radio-quiet X-ray binaries: LSI+61 303"
Massi, M.
2004, evn conf, 215 (arXiv:astro-ph/0410502)
34)"Results of a search for new microquasars in the Galaxy"
Ribó, M.; Paredes, J. M.; Martí, J.; Casares, J.; Bloom, J. S.; Falco, E. E.; Ros, E.; Massi, M
 2004, RMxAC, 20, 23
33)"Sub-arcsecond radio structure of LSI +61 303"
Massi, M., Ribo`, M.; Paredes, J. M., Peracaula, M., Marti, Garrington, S. T.
 2002, Fourth Microquasars Workshop,Cargèse, 2002. Ed. Ph. Durouchoux, Y. Fuchs, and J. Rodriguez. Pub. Center for Space Physics: Kolkata (India), p. 230.
 32)"Investigation of magnetic loop structures in the corona of UX Arietis"
 Massi, M.  & Ros, E.
  2002, 6th European VLBI Network  Symposium, eds. E. Ros, R. Porcas, A. Lobanov, A. Zensus 275-276
  31)"Radio jets in the high mass X-ray binary LSI +61 303"
Massi, M., Ribo`, M., Paredes, J. M., Peracaula, M.,Marti, Garrington, S. T.
 2002, 6th European VLBI Network Symposium, eds. E. Ros, R. Porcas, A. Lobanov, A. Zensus 271-272
  30)"EVN and MERLIN confirmation of the LS 5039 jets"
Paredes, J. M., Ribo,` M., Ros, E., Marti, Massi, M.
  2002 6th European VLBI Network Symposium, eds. E. Ros, R. Porcas, A. Lobanov, A. Zensus 277-278
  29)"EVN and MERLIN observations of microquasar candidates"
 Ribo`, M., Ros, E., Paredes, J., Massi, M. \&  Marti
 2002, 6th European VLBI Network Symposium, eds. E. Ros, R. Porcas, A. Lobanov, A. Zensus 279-280
28)"Microquasars as possible counterparts of unidentified EGRET sources"
Paredes, J. M., Marti, J., Ribo, M., Massi, M.
  2002 MmSAI 73, 900
27)"One-sided elongated feature  in LSI 61303"
M. Massi, M. Ribo´, J. Paredes, M. Peracaula, R. Estalella
2001,Astrophysiscs and Space Science Suppl. , vol. 276, 125
26)"Identification of 3EG J1824-1514 as a radio jet X-ray binary"
J. Paredes, J. Martí, M.  Ribó, M. Massi
2001, Astrophysiscs and Space Science Suppl. , vol. 276, 79
25)"Microquasars and unidentified - EGRET sources: the case of LS 5039"
J. M. Paredes, J.  Martí, M. Ribó, M. Massi
2001 Nugh. Conf. 263
24)"Coordinated BeppoSAX and VLA observations of UX Arietis "
Franciosini, E.; Pallavicini, R.; Bastian, T.; Chiuderi-Drago, F.; Randich, S.; Tagliaferri, G.; Massi, M.; Neidhöfer, J.
2001 ASPC, 223, 930
23)"Radio Jets in LS 5039"
J. M. Paredes, J.  Martí, M. Ribó, M. Massi
2001, ApSSS, 276,79
22)"Discovery of a Microquasar with High-Energy Gamma-ray Emission"
J. M. Paredes, J.  Martí, M. Ribó, M. Massi
2000, Gamma ray Astronomy SYMPOSIUM, Heidelberg. AIP proc. 558, 745
21)"LS 5039, a Microquasar with Persistent Radio and γ-ray Emission"
Ribó, M.; Paredes, J. M.; Martí, J.; Massi, M.
2000,yerac conf. 44
20)"The milliarcsecond radio structure of LS5039"
J. M. Paredes, J.  Martí, M. Ribó, M. Massi
2000, 5th European   European VLBI Network Symposium, eds  J.E. Conway, A.G. Polatidis, R.S. Booth and Y.M. Pihlström, pub. Onsala Space Observatory, p. 163
19)"New results on LSI 61303 and Cygnus X-3"
 J. M. Paredes,M. Peracula ,J.  Marti', R. Estalella , M. Massi
 Vistas in astronomy, vol. 41, Part 1, 49 (1997)
18)"High dynamic range imaging with the EVN"
K. Leppänen,M. Massi, M. Rioja, H. Sanghera
Vistas in astronomy, vol. 41, Part 2  (1997)
17)"Non-closing errors in EVN data"
M. Massi, M. Rioja, D. Gabuzda, K. Lepp"anen, H.  Sanghera, K.  Ruf, L. Moscadelli
Vistas in astronomy, vol. 41, Part 2 (1997)
16)"Rising Phase in UX Arietis Radio Flares"
G. Torricelli-Ciamponi, E. Franciosini ,M. Massi ,J. Neidhöfer
 ASP Conference Series  93, p. 339 (1996). Ed. Taylor and Paredes
15)"Searching for Extended Radio Emission around LS I +6l degrees 303"
Paredes, J. M.; Marti, J.; Peracaula, M.; Estalella, R.; Massi, M.
 ASP Conference Series. 93, p. 246 (1996). Ed. Taylor and Paredes
14)"Radio observations of UX Arietis: analysis of its variability."
M. Massi, J. Neidhöfer, G. Torricelli-Ciamponi , F. Chiuderi-Drago
 ASP Conference Series. 93, p. 330 (1996). Ed. Taylor and Paredes
13)"Systematic Radio-Observations of UX Arietis"

G. Torricelli-Ciamponi
,J. Neidhöfer ,M. Massi , Chiuderi-Drago F.
 IAU Coll. 151, 454, 42, (1995)
12)"VLBI observations of LSI+61° 303"
Paredes, J. M.; Massi, M.; Estalella, R.; Felli, M.
1993,sara conf 24.
11)"Dynamic range improvement of high resolution radio maps. Part I: removal of the polarization impurity error"
M. Massi
1993, MmSAI 64, 1031 
10)"Properties of H2O masers from the Arcetri atlas"
Comoretto et al.
1991 Molecular Cloud  Conf.  203
9)"Properties of H
2O masers from the Arcetri atlas"
Tofani et al.
1991, ASPC, 16,89
8)"VLBI observations of WR stars"
M. Felli, M. Massi
IAU Symposium 143, p.87 (1990). Ed.  K.A. Van der Hucht and B. Hidayat
7)"Variations of VLBI structure  in UXAri."
M. Catarzi, M. Felli, M. Massi, F. Palagi, R. Pallavicini, G. Tofani.
IAU Symposium  129,  p. 283 (1987). Ed. M.J. Reid and J.M. Moran
6)"Evaporating Protostellar Disks Around Low-Mass Stars in the Core of Orion?"
Churchwell, E.; Wood, D.; Felli, M.; Massi, M.
 1987, BAAS, 19, 952
5)"High Resolution Observations of NH3 and H2O Line Emission in M17"
Churchwell, E.; Felli, M.; Massi, M

1986, BAAS, 18, 671
4)"Induced star formation in M17. High resolution NH3 and IR observations."
M. Felli, M. Massi, R. Stanga, E. Churchwell.
IAU  Symposium  115,  p. 141 (1985). Ed. M. Peimbert and J. Jugaken
3)"MonR2: a blister type HII region."
M. Massi, M. Felli, M. Catarzi, M. Simon.
IAU  Symposium  115,  p. 193 (1985). Ed. M. Peimbert and J. Jugaken
2)"An Analysis of M17 Based on VLA Synthesis Maps at 1. 3, 2, 6, and 21 cm"
Churchwell, E.; Felli, M.; Massi, M,

1983, BAAS, 15, 680
1)"Räumlich hochaufgelöste Beobachtungen an S106 von λ = 0.6 μm bis λ = 1.3 cm. Ein Windmodell des bipolaren Nebels"
Felli et al.
1983 MitAG, 60, 321

  Technical Reports

15)"Preliminary Study on the Influence of the Instrumental Polarization on Geodetic Data "
 Sorgente M.  and M. Massi
EVN Doc. n.107, 2000
14)"Status of the EVN Instrumental Polarization "
 M. Massi.
EVN Doc. n.91, 1999
13)"Investigation on the Origin of the High Instrumental Polarization at the Medicina Telescope"
M. Massi, K. Ruf, A. Orfei
EVN Doc. n.85 , 1998
12)"Project for a Digital Polarimeter.Part I: Relationship between   D terms and the  instrumental polarization  vector"
M.  Massi, G. Tuccari , S.  Orfei
EVN Doc 81, 1997
11)"Stability  of the EVN  D-terms"
M. Massi  and  S.  Aaron
EVN Doc. n. 77, 1997
10) "High Dynamic Range Imaging with the EVN"
M. Massi  and  S. Aaron
EVN Doc. n. 75, 1997
9)"Analisi di dati spettrali con package di riduzione TOOLBOX su workstation di tipo SUN"
R. Cesaroni, G. Comoretto,M. Massi, F. Palagi.
Tech. report Oss. Arcetri n. 5/1988
8)" DRAW2: un software per la radiospettroscopia. Implementazione   Vax ed applicazioni "
M. Massi, G. Comoretto, A. Damiano, F. Palagi, G. Tofani, M. Felli
Tech. report Oss. Arcetri, Maggio 1986
7)"Manuale per la gestione  tramite Field System  di una osservazione VLBI"
M. Massi
Tech. report Oss. Arcetri, Maggio 1985
6)"Progetto Autocorrelatore Digitale. Prima prova astronomica  dell'autocorrelatore digitale a larga banda di Arcetri"
M. Catarzi,G. Comoretto, P. Curioni, M. Damiano, M. Felli,M. Massi, S. Misuri, D. Panella, F. Palagi, N. Speroni, G. Tofani
Tech. report Oss.Arcetri, Marzo 1985
5)"Software di interfaccia fra HP-1000 e ACU dell'antenna VLBI"
G. Comoretto,M. Massi, S. Misuri, F. Palagi e G. Tofani
Tech. report Oss.Arcetri, Feb. 1984
 4)"Tecniche di misura in radiospettroscopia. Parte I"
M. Massi
Tech. report Oss.Arcetri, Giugno 1984
3)"Software per il puntamento dell'antenna di 32m (progetto VLBI). Parte I"
G.Comoretto, M.Massi, F.Palagi
Tech. report Oss.Arcetri, Dicembre 1982
2)"VLBI data reduction programs"
Tech. report Oss.Arcetri, Marzo 1982
1)"An introduction to continuum VLBI "
Tech. report Oss. Arcetri, Maggio 1981